case study of acid rain in australia

• Distillations Podcast

Distillations podcast

Whatever Happened to Acid Rain?

It’s complicated.

Remember acid rain? If you were a kid in the 1980s like our hosts were, the threat of poison falling from the sky probably made some kind of impression on your consciousness. But thanks to the work of scientists, government, the media, and the pope—that’s right, the pope—the problem was fixed! Well, mostly fixed is probably more accurate.

This complicated story spans 27 years, six U.S. presidents, and ecologist Gene Likens’s entire career. Discover the insidious details in the second chapter of our three-part series on environmental success stories. 

Hosts : Alexis Pedrick  and Elisabeth Berry Drago Senior Producer :  Mariel Carr Producer :  Rigoberto Hernandez Audio Engineer:  James Morrison   Additional audio was recorded by David G. Rainey. Image of Gene Likens by Phil Bradshaw of FreshFly . Our theme music was composed by Zach Young.  Additional music courtesy of the Audio Network . 

Research Notes

We interviewed Rachel Rothschild, a former Science History Institute research fellow and Rumford Scholar, about her book, “Poisonous Skies: Acid Rain and the Globalization of Pollution.” To research this episode we read her 2015 dissertation, A Poisonous Sky: Scientific Research and International Diplomacy on Acid Rain . We also read  Merchants of Doubt: How a Handful of Scientists Obscured the Truth on Issues from Tobacco Smoke to Global Warming  by Naomi Oreskes and Erik Conway (Bloomsbury, 2010).

We interviewed Gene Likens at Hubbard Brook Experimental Forest in New Hampshire in 2015 with Glenn Holsten and FreshFly . We interviewed him again in May 2018.

These are the archival news clips we used as they appear in the episode:

The following are the archival news clips we used as they appear in the episode:

Bettina Gregory, Tom Jarriel, and Bill Zimmerman. ABC Evening News , December 14, 1978. 

Walter Cronkite and Jim Kilpatrick. “Environment: The Earth Revisited/Acid Rain.” CBS Evening News , September 11, 1979.

Robert Bazell and John Chancellor. “Special Segment: Acid Rain.” NBC Evening News , May 9, 1980.

“The MacNeil/Lehrer Report: Acid Rain,” NewsHour Productions, American Archive of Public Broadcasting (Boston: WGBH; Washington, DC: Library of Congress), aired May 26, 1980, on PBS, http://americanarchive.org/catalog/cpb-aacip_507-pk06w9754b.

“The MacNeil/Lehrer NewsHour,” NewsHour Productions, American Archive of Public Broadcasting (Boston: WGBH; Washington, DC: Library of Congress), aired on June 30, 1988, on PBS,  http://americanarchive.org/catalog/cpb-aacip_507-b56d21s53c.

Tom Brokaw and Robert Hager. “Air Pollution: George Bush.” NBC Evening News , November 15, 1990 .

ABC Evening News, December 14, 1978: In the Adirondack Mountains of New York the lakes are so clear they mirror the forest around them. One might think pollution could never taint this mountain paradise, but it has. The fish have died in this lake. The rain has turned the water acid. Scientists say particles of sulfur are carried by these clouds and when it rains it pours a mild sulfuric acid into lakes like this one. The experts say power plants discharge most of the sulfur into the air. And what goes up these smoke stacks, must come down.

Alexis : Hi, I’m Alexis Pedrick.

Lisa : And I’m Lisa Berry Drago, and this is Distillations , coming to you from the Science History Institute.

Alexis : Each episode of Distillations takes a deep dive into a moment of science-related history in order to shed some light on the present. Today we’re talking about acid rain, in the second installment of a three-part series about environmental success stories.

Lisa : Our last episode, “Whatever Happened to the Ozone Hole?” is available on our website: Distillations DOT ORG, through Apple Podcasts, or wherever else you get your podcasts!

Alexis: In the early 1960s American scientists discovered a new environmental threat called acid rain, but most people didn’t become aware of it until almost 1980. Lisa, do you remember learning about acid rain?

Lisa : Yeah, but I’m not sure I knew what it was when I was a kid. I think I thought it had something to do with Guns N’ Roses, sort of acid-washed jeans, November rain…

Alexis : Same. Same. I think I had to do a school project on it and I remember reading this book about acid rain and all these terrible things that happened with it. But then it was raining outside and I was fine. And I didn’t melt. So I had no concept of, ‘is this a threat or not?’.

Lisa : Right. We definitely got rained on in the 80s.

Alexis : Right. And we survived. So…

Lisa : So why didn’t we find out about this problem sooner? What happened in this nearly two- decade-long gap? And what led to that ABC evening news clip we just heard from December of 1978?

Alexis: If you listened to our show about the ozone hole, you’ll remember that we told you how to solve any environmental problem in five easy steps.

Lisa : And of course…we actually learned that it’s far more complicated than that, but we’re going to follow the steps again anyway.

Alexis : So here we go: step number one: figure out the problem.

Lisa : Step two: get your evidence.

Alexis : Step three: inform the public.

Lisa: Step four: you have get industry onboard

Alexis: Step five: implement policy.

Lisa : Acid rain took a long time to resolve in the United States, and there were a lot more roadblocks and slowdowns than with the ozone hole, but you’re gonna hear all of it, so let’s get started.

Chapter 1: Figure out the Problem

Lisa: Chapter One. Figure out the problem.

Alexis : Compared to the ozone hole, acid rain took a bit longer to get under control in the U.S.

–like, a couple decades longer. It was first discovered in North America in 1963, but it took until 1980 before the media really jumped in, and until 1990 until there was any kind of resolution.

Ecologist Gene Likens was there the whole time. And we met up with him where it all started. In a pristine forest in the mountains of New England.

Likens: I’ve always said that I can’t believe that I’ve been paid for all these years to work here. I mean come on! It’s too nice, it’s too beautiful and yet they pay me to work here.

Alexis: Gene Likens is standing by a stream in Hubbard Brook Experimental Forest, in the White Mountains of New Hampshire. These woods have been his laboratory since 1953. When they set up Hubbard Brook, Likens and his colleagues thought of themselves kind of like doctors, and the forest ecosystem as a patient.

Likens: We had the idea that we could use the chemistry of the water flowing out of this watershed ecosystem much like a physician uses the chemistry of our blood and urine. If the physician measures the chemistry of my blood or urine and sees that something is wrong then he has some idea that my system isn’t functioning properly.

Alexis : In 1963 Likens and his colleagues were looking at the rain. And what they found was startling.

Likens : This is where we discovered acid rain. Our very first samples was roughly 100 times more acidic than we thought the rain ought to be. We didn’t have any idea why it was so acid or where it might have come from or how long it had been there? We didn’t know any of those fundamental answers.

Alexis : Likens found some of those answers by connecting with another scientist on another continent. Just a handful of years after his discovery, Likens crossed paths with a scientist in Sweden who had recently discovered acid rain in Scandinavia. His name? Svante Oden.

Likens: And Svante said, “I’m going tonight on the overnight train from Stockholm to Oslo, Norway, and would you like to go along?” And I said “oh sure, why not?” So we took the overnight train together, and sat up and talked most of the night.

Alexis: Oden told Likens that he thought that the pollution in Scandinavia was coming from more industrialized parts of Europe, and this information helped Likens connect some dots.

Lisa : It’s like he had to talk to someone else from across the globe to understand what was happening in his own little corner of the world. And this is a bigger theme in science I think we hear again and again. You have to step outside of your framework to see the big picture.

Alexis : Exactly. No one is ever just working on one thing in isolation by themselves. Lots of people are working on the same thing all over the world and they benefit from talking to each other.

Likens: It was just one of those serendipitous events where something happens and helps you understand what’s going on much more clearly than you might’ve otherwise.

Alexis: Likens went back to the U.S. and continued monitoring acid rain. Then in 1974, eleven years after he first discovered it, he decided he had enough evidence to write an article with his colleague Herbert Bormann for the academic journal Science . It was called “ Acid Rain: A Serious Environmental Problem .” By this point Likens had moved to upstate New York and had also found acid rain in the Adirondacks.

Likens: The paper was saying, “This is not something unique to Hubbard Brook but is a much more regional problem.”

Alexis : The paper said that acid had been falling in the Northeast for 20 years. But the biggest revelation was that tall smokestacks hundreds of miles away in the Midwest were to blame.

Emissions from burning coal was a major source of the problem.

Likens: The Midwest is emitting large quantities of sulfur and nitrogen Oxides. It gets carried to the atmosphere and then deposited here whenever it rains and snows. So it’s like somebody throwing their garbage out and then the garbage falling on your property and you don’t like it much.

Alexis : The idea that pollution could travel such distances was a new revelation. And the irony of it all was that the culprit—those tall smoke stacks—were originally created as a solution to another pollution problem.

Donora, Pennsylvania News Clip: Residents have difficulty breathing the murky air. 20 died. 400 others are stricken with respiratory illness. A local zinc plant is suspected of emitting poison smoke is closed down. An epidemic of pneumonia is feared in the wake of Donora’s deadly rain of smog.

Alexis : Donora was a small mill town in western Pennsylvania. Back in the 1940, their zinc plant, like most plants at the time, had a short smoke stack, and it was pumping out a poisonous combination of carbon monoxide, sulfur dioxide, and metal dust. In 1948 the town suffered a smog attack that killed twenty people and made seven thousand more sick. The disaster alerted people to the hazards of air pollution, and it eventually helped trigger the 1970 Clean Air Act. But it also raised the height of smokestacks.

Lisa : Tall smokestacks helped towns like Donora, they whisked clouds of pollution out of their backyards. But unfortunately they just sent them to other people backyards, further away.

Likens : And what that really did was convert a local soot problem to a more regional soot problem. It just took the push from here and emitted it at a higher level and then it was swept away by the winds and the atmosphere.

Chapter 2: Get Evidence Alexis: Chapter 2: Get evidence.

Lisa : By the time Gene Likens and Herbert Bormann published that paper in 1974, they’d been monitoring the issue for more than a decade.

Alexis : So maybe you’re wondering what they were doing all that time. I mean we certainly were.

Lisa : The answer is gathering that evidence. First they went to some of the most remote places in the world to try to get a baseline estimate of what the acidity, or pH, of rain should be. They had to go places without human activity or any smokestacks—tall or short. Just a few of the places they went were Southern Chile and remote parts of China and Australia. They traveled for a month by boat to get to an island in the middle of the Indian Ocean called Amsterdam Island.

Through it all they learned that the default pH of rain is 5.1. The samples they were measuring back home were at least a hundred times more acidic than that. Here’s how an ABC news clip explained what these numbers meant.

ABC Evening News, December 14, 1978: A pH of 7 would be neutral, the lower the reading the more acidic it is. This sample of rainwater from the summit reads 3.3, which is just about as acidic as grapefruit juice.

Lisa : Likens’s world travels really proved that the rain truly was too acidic. His research also proved that the pollution that caused acid rain really was coming from industry in the rust belt.

Likens : We tried to follow isotopic tracers in the emissions from smokestacks in the Midwest. We followed plumes in small airplanes and vehicles on the ground. We went to enormous lengths to try to answer those questions.

Lisa : Ten years in it seemed like the science was pretty clear. Likens and his team felt confident in their research and they published their article. Some of what they hoped for started to come true. The New York Times quickly picked up their story and the scientific community in the U.S. started paying attention to acid rain.

Likens: That paper changed my life forever because it was published on the front page of the New York Times . I had colleagues all over the world calling me saying, “Likens, what is this? What’s going on?”

Lisa: Environmental scientists definitely took notice. But so did plenty of other people, many with their own agendas.

Likens : There was lots of pushback saying, “Well, it’s not us.” You know, “We didn’t do it. It’s not us. There is no such thing as acid rain.” I can remember many times when there would be a meeting or I might be giving a talk and someone, a denier type would stand up and say, “There’s no such thing as acid rain.” And I would say, “Have you ever collected a sample of rain and analyzed it?” The answer was always no. I said, “Try it sometime. You might be surprised what you find out.”

Rachel Rothschild: There was this pretty dramatic response from the coal industries, who were thought to be the most serious contributors to the problem.

Lisa: Rachel Rothschild is a historian of environmental science and technology and a former research fellow at the Science History Institute. She’s finishing up a book called Poisonous Skies: Acid Rain and the Globalization of Pollution. She’s studied the pushback against acid rain science, and one of the things she’s uncovered is how quickly the coal industry realized that

Likens’s research could be a threat to them.

Rothschild: They, in fact, launched some of the most serious and extensive research efforts on acid rain in the hope of vindicating themselves, and it set up a very interesting confrontation between industry scientists and environmental scientists in the late 1970s and into the 1980s.

Lisa : So we’ve been here in step two, gathering evidence with Gene Likens, thinking we were alone with him.

Alexis : But it turns out these steps—which we made up by the way—aren’t secret! Other people can jump in and gather evidence too!

Lisa: So with acid rain step two is multi-pronged: first you have to gather your evidence, then wait for someone else to dispute or distort it, and meanwhile they’re gathering their evidence, and then you have to dispute the counter-evidence. When the attacks came they were often aimed right at Gene Likens.

Likens: It was bad. It was really nasty. I had a contract put out on me. It was…Did I tell you this story before? If so I apologize. Oh my goodness, I hadn’t thought about any of this in a long time, really painful.

Lisa : A coal-backed policy group tried to carry out what we can only describe as a “scientific hit” on Gene Likens. Okay, maybe that’s a little extreme, but they put out a call to discredit his research on acid rain—they called him by name—and offered to pay four hundred thousand dollars to anyone who could do the job.

Likens : That was the call. Show that he is wrong. So yeah, it was pretty unsettling and pretty shocking. It wasn’t a contract on my life, but it was a contract on my career, which in some ways almost was as important as my life. I mean, not really but you know what I mean? It’s what I do. It’s what I am. It’s what I’m all about. I grew up on a small farm in northern Indiana. I was a farm boy. I just thought the world worked a little differently and I kept finding out it didn’t. I thought all this

science rode around like knights on big white horses and I found out it didn’t work that way. Answers could be purchased and they were. All that was greatly disturbing to me.

Alexis : So I think this is a good place to stop because this is a pattern we’ve seen before, right?

The naiveté of scientists playing by the rules, but they don’t really understand all of them. Or

they see rules that aren’t there. They are just in their lab doing their thing and not really thinking about how to play this larger game.

Lisa : What happens when the research hits the real world? Yeah, the game can change a lot.

Alexis : Exactly.

Lisa : It’s partly that naïve sense of playing by the rules maybe? That might help certain scientists when they get to a crisis point, because in the end they have the science to go back to.

Likens: Why did we keep persevering? [laughs] Because I’m a scientist and because I am searching for the truth and because in science we search for the truth. We rarely find it, but we search for the truth.

Lisa: The contract Likens is talking about was put out by one of the biggest sources of counter- research—a coal trade group called the Edison Electric Institute. Their research arm was called EPRI, or the Electric Power Research Institute. Their job was to refute any science that made them look bad, and they were desperate to find some other industry to blame acid rain on.

Rothschild: They were hoping that they might find that, say, logging or other forestry practices, for example, might result in increased acidity in the soil.

Lisa : So EPRI scientists conducted a study in the Adirondacks to get alternative evidence, alternative facts if you will, but they couldn’t find any. So they distorted the evidence.

Rothschild: I would say they misrepresented the evidence and tried to convey that there was more uncertainty than there actually was and tried to use evidence that simply supported a different kind of proposition, to say that actually acid rain wasn’t the problem at all.

Lisa : That scientific hit never paid off. Remember how Gene Likens spend those eleven years of gathering evidence?

Likens: It all started with measurements and was bolstered by continuing high quality measurements so that when the attacks came we were able to lay our data out there and say, “Go at it and show that it’s wrong,” and nobody was ever able to do that.

Chapter 3: Let the Public Know

Lisa: Chapter three. Let the public know.

Alexis : Gene Likens learned that his data was crucial, but it was not going to speak for itself. So he had to learn how to talk to the public and the naysayers. When he wrote that pivotal paper in 1974 he consciously chose the term “acid rain” because he thought it would get people’s attention, and he was right.

Likens : We thought and argued long and hard about whether we should use that as a title. I’m really glad that we did because it brought public attention to the issue in ways, and I’m a scientist, so I’m not supposed to care about that, but in terms of the management of this serious environmental issue it helped. Because you can walk in the rain, you can sing in the rain, you can dance in the rain, but if the rain is acid you might think about it very differently than you would have otherwise.

Alexis: In the late 70s and early 80s television played a crucial role in getting the American public to know and care about acid rain. Robert Bazell worked at NBC news for 38 years. He was the chief science correspondent during the 1980s.

Robert Bazell : Well the media landscape was that there were three networks and most of America watched one of the three every night. There was no cable television.

Newspapers were not going out of business for all the things we think about now. And of course, there was no Internet. It was a very different world, and there was an enormous amount of impact from those stories that were on television.

CBS Evening News, September 11, 1979: Well, as far as I’m concerned the lake is dead. Period. There’s no swallows around, the swallows have left almost two weeks early this year.

Alexis: This is one of the earliest stories on Acid Rain, from 1980.

NBC Evening News, May 9, 1980: Now there are no fish, no lily pads. In fact, there is no life visible in Woods Lake. It was killed by a new type of pollution which is affecting many parts of the world. It’s called acid rain.

Alexis : 38 years later Bazell still remembers reporting it.

Bazell: We were always looking for stories, and this one was an important one, obviously, for the reasons that you just heard in that clip. Fish were dying, trees were dying. It was a visual story, which makes it very impactful for television. Made it a very easy story to tell. You could see what was happening, it wasn’t an obscure concept.

Alexis : Everyone was talking about acid rain, from TV reporters—like Robert Bazell—to cartoons, to the Pope. That’s right, the Pope. In 1985 Gene Likens visited Pope John Paul II, who went on to address acid rain in his encyclical. So the media helped. But it also might have hurt.

The MacNeil/Lehrer Report, May 26, 1980 [Jim Lehr] : There is a new environmental fear alive in the land, the fear of something called “acid rain.” Reports of its presence and its danger come from everywhere.

Alexis : This is Jim Lehrer, in a 1980 clip from the Macneil/Lehrer Report , the precursor to PBS Newshour . On the show Lehrer holds what is basically a debate. On one side is Douglas Costle, Jimmy Carter’s EPA administrator, and on the other is a man named William Poundstone. He’s the executive vice president of Consolidated Coal—one of the country’s biggest coal companies. Throughout the show Costle lays out well-established facts about acid rain and Poundstone disputes them. Or more accurately, he evades and distorts them.

The MacNeil/Lehrer Report, May 26, 1980 [Charlayne Hunter-Gault] : Mr. Costle, what has brought you to your present state of alarm?

Douglas Costle: I think the single most important thing that happened this year was that scientists from all around the world came to me and they said, in effect, “there`s a lot we still do not know about acid rain, but we know enough now to know that we should not be making the problem worse.”

Lehrer : Mr. Poundstone, what do you think of Mr. Costle`s position on acid rain?

Poundstone : There is no issue that the rainfall is acid. But we go beyond that point, and we start to diverge.

Lehrer : In other words, you will concede that there is such a thing as acid rain?

Poundstone : Yes, sir. The rain—

Lehrer : And it’s a damaging—it has serious repercussions when it hits the ground?

Poundstone : I have not said that. I have said the rain is acid.

Lisa and Alexis: “Ohhhhhhh” do you see what’s going on here? I think we can all see what’s going on here.

Poundstone : And there’s a great deal of argument and evidence that must be heard on this issue. The English Electricity Board, the EPRI people as well—

Lehrer : Who are the EPRI people?

Poundstone : That is the research arm of the Electric Power Research Institute.

Lehrer : I see. All right.

Poundstone : They have some $22 million a year in research activity, and I think in these areas are doing more than anyone.

Alexis: Poundstone’s goal was to discredit acid rain science, and this interview made it seem like there was no scientific consensus at all. If you’ve been paying attention to this podcast you already know this is what EPRI was all about. But Jim Lehrer takes everything both men say at face value, seemingly encouraging his viewers to do the same. Imagine you’re sitting at home watching this on the news, they’re the same to you. But they’re not the same.

Lisa : We see this kind of false equivalence all the time. Especially with environmental issues.

Alexis : Right, so that’s why Douglas Costle spent a lot of time playing defense during the Lehrer interview, but he still managed to squeeze in the fact that there was an attainable solution: older power plants could be retrofitted with a technological fix to reduce their emissions.

Lisa : I’m just speculating here, but it seems like that interview must have caught him off-guard, like it felt like a big setback. Just three weeks after this interview Douglas Costle said this on the ABC evening news:

ABC Evening News, June 18, 1980 [Douglas Costle]: I don’t want to sound too cynical, but I have never seen an industry that is a part of the problem, be the first to acknowledge a problem. Or the extent of their own involvement in it.

Alexis : Despite all of this it seemed like things were moving ahead. President Carter signed the acid precipitation act of 1980, which promised to address the problem within ten years. Things were looking up. And then this happened.

Ronald Regan Election Speech Jan. 20. 1981: In this present crisis, government is not the solution to our problem; government is the problem.

Chapter 4: Implement Policy

Alexis : Chapter four. Implement policy.

Lisa : Or, in the case of acid rain: intentionally waste a decade not implementing any policy!

Alexis: It turns out elections have consequences.

Rothschild: So Reagan had really campaigned, much like President Trump did recently, on this idea of deregulating the environment and making sure that environmental regulations weren’t getting in the way of economic development and growth. When he came into office, he very quickly transformed the Environmental Protection Agency.

Lisa : Douglas Costle didn’t last long in Reagan’s EPA. Instead the president brought on one of EPRI’s top scientists—remember them? Another new EPA pick banned the use of the term acid rain. In short, Reagan was not good for the environment. He did, however, invite a team of scientists to brief him on the issue at the White House in 1983. The group was led by Gene Likens.

Likens : At the end, President Reagan sat back in his chair and he looked around the room and he said, I’ll never forget this quote, “Well, gentleman it’s clear to me that my undergraduate education did not prepare me for such complicated issues.” I thought, “Wow.” But any rate we made our case and that was in September of 1983 and on January the Director of Management and Budget made the pronouncement that, “no, we’re not going to deal with acid rain. It’s too expensive to do so. We’ll study it instead.”

It was an amazing experience to go to the White House and to brief the president and the full cabinet, but not to see something happen.

Lisa : In 1986 Reagan suffered a backlash in the midterm elections, and results sent a message that he needed a different approach to environmental issues. So he signed the Montreal Protocol for the ozone hole, and the Sophia Protocol, an international accord aimed at reducing nitrogen oxides to combat acid rain. The environment became a huge campaign issue in the 1988 election.

Michael Dukakis attack ad: For seven and half years George Bush personally weakened regulations on corporate polluters. And now suddenly George Bush tells you he is going to be the environmentalist president. Do you believe that?

Lisa : On the left was Michael Dukakis, who obviously did not win. But Rachel Rothschild says he made a lasting impact.

Rothschild: So, Dukakis really placed environment at the forefront of his political platform during the election, and in many ways forced President Bush to move to the left on that issue and make a decisive break with President Reagan.

Lisa: Part of the public’s anxiety was a growing awareness of something called global warming.

Rothschild: In the summer of 1988 there were congressional hearings about the possibility that carbon dioxide was increasing the planet’s temperature with the potential for catastrophic results to the environment.

The MacNeil/Lehrer Report, June 30, 1988 Congressional hearing [Daniel Albritton, NOOA] If greenhouse gases continue to grow unabated…

[Rep. Claudine Schneider [R] Rhode Island]: There is a very high, high risk of irreversible, and catastrophic impact looming on the horizon.

Rothschild : And that I think, for the first time for many Americans, raised the specter of large scale planetary threats from fossil fuels. And so acid rain, in comparison, almost seemed much more solvable.

Likens: I often wondered if I was just banging my head against the wall for no value. But that didn’t turn out to be the case, did it? Because in 1990 under amazing conditions a Republican president signed the 1990 Clean Air Act into legislation.

NBC Evening News, Nov 15, 1990: What the President is calling for would be the first improvement of the clean air law in 12 years.

President George H. W. Bush : We’ve seen a stalemate. It’s time to clear the air. Acid rain must be stopped and that’s what we all care about.

President George H. W. Bush, address to Congress February 9, 1989: Because the time for study alone has passed and the time for action is now.

Likens : The Congress, both the House and the Senate had voted overwhelmingly, it wasn’t unanimous, but it was overwhelmingly in favor of that action, the 1990 Clean Air Act Amendments. So being able to be there in 1963 and make the discovery for North American about the occurrence of acid rain, and then all those tough years in between to 1990 when our country took legislative action, was very satisfying, and maybe is unique. I don’t know.

Lisa : Bush implemented what is now known as “cap-and-trade.” It essentially lets companies buy and sell the rights to pollute. It was a perfect free-market solution for a Republican, environmentalist president.

Alexis : You might have noticed that we left out the “get industry on board” step, that’s because, well, they never really got on board, per se, eventually they just had to yield to the change in policy.

Chapter 5: What Does Success Look Like?

Alexis: The cap and trade program was a cost-effective solution, and it stemmed the worst environmental impacts. The rain at Hubbard Brook is 80% less acid now than it was in 1963. But there are still areas of the country that are still at risk or haven’t fully recovered, so it’s a success story, but it’s complicated.

Lisa : The lesson of Gene Likens is the same lesson of Hubbard Brook forest. The mountains of New Hampshire do not exists in a vacuum and neither does Gene Likens and his science.

Alexis: Right. Exactly. And we’ve seen this—

Lisa: Both of them are touched by industry, and social concerns, and money and power and all of that stuff.

Alexis : And by the way, Gene Likens still has not given up the fight.

Likens: No way. And I still don’t. I’m in my mid-eighties and I’m not giving up yet. Here I am talking to you.

Alexis : Distillations is more than a podcast. We’re also a multimedia magazine.

Lisa : You can find our videos, our blog, and our print stories at Distillations DOT org.

Alexis : And you can also follow the Science History Institute on Facebook, Twitter, and Instagram.

Lisa : This episode was produced by Mariel Carr and Rigo Hernandez. Additional sound was recorded by Dave Rainey.

Alexis : This show was mixed by James Morrison and our theme music was composed by Zach Young.

Lisa : For Distillations I’m Lisa Berry Drago.

Alexis : And I’m Alexis Pedrick.

Alexis and Lisa : Thanks for listening!

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• News & Insights
• Media Coverage

The bittersweet story of how we stopped acid rain

Cary's Gene Likens' discovery of acid rain in 1963, set the collective wheels in motion to raise awareness and isolate the cause of acid rain. Not just in North America, but across the industrialized world.

Photo by NatureLifePhoto

• Acid Rain ,
• Environmental Policy

Acid rain went from being a pollution disaster to an environmental success story. How did scientists manage to prove that acid rain existed, and find a way to stop it?

A group of kids canoeing in Canada’s Killarney Provincial Park are paddling across a serene and unnaturally turquoise lake. It’s a hot sunny day, and a thirsty boy dips an aluminium cooking pot into the water to refill his fellow canoeist’s canteens. In a momentary lapse of concentration, the pot slips from his grasp. As it sinks underwater beyond reach, what’s incredible is that it’s visible all the way down to the lake floor some 50ft (15.2m) below.

It’s the mid-1980s. One of the kid canoeists is me, and there’s an unfortunate explanation for this water clarity. This lake, near the nickel and copper smelters of the town of Sudbury, Ontario, has been radically altered by acid rain. Almost every living thing in the water – like the tiny algae that would normally block light from reaching the depths – has gone, leaving the water here and in lakes across the region a beautiful but eerily lifeless aquamarine.

Fast forward to 2019 and another set of lakes in a remote corner of north-west Ontario. Biologist Cyndy Desjardins is sipping coffee at breakfast following a nocturnal boat trip at the International Institute for Sustainable Development’s Experimental Lakes Area (IISD-ELA). Smiling but sleepy, she spent much of the night working in nearly pitch-dark conditions, surveying for tiny monster-like creatures: freshwater opossum shrimp called Mysis relicta. Desjardins is part of a team attempting to close the loop on an acid rain experiment that began in the 1970s.

Bitter controversy

At its worst, acid rain stripped forests bare in Europe, wiped lakes clear of life in parts of Canada and the US, and harmed human health and crops in China where the problem persists. Looking back today, there is little argument that the cause was sulphur dioxide and nitrogen oxides emitted by fossil fuel combustion by cars and industrial facilities like smelters and coal-burning utilities. When combined with water and oxygen in the atmosphere, these air pollutants chemically transform into sulphuric and nitric acid. Acidic droplets in clouds then fall as rain, snow or hail.

We know this now. But for a long time, acid rain was a puzzle. In 1963, as part of a long-term ecosystem study that is still ongoing today, Gene Likens collected a sample of rain at the Hubbard Brook Experimental Forest in New Hampshire’s White Mountains. That sample was “about a hundred times more acidic than we thought it should be”, says Likens, now emeritus professor in ecology at the Cary Institute of Ecosystem Studies in Millbrook, New York. His discovery back in 1963, on the heels of work dating back to 1872 and even earlier, set the collective wheels in motion to raise awareness and isolate the cause of acid rain. Not just in North America, but across the industrialised world.

Other crucial evidence that led to action on acid rain – on both sides of the Canada-US border – came from experiments at north-west Ontario’s Experimental Lakes Area (ELA). Its soft-water lakes were far enough from sources of pollution that they had escaped the effects of acid rain, acting as a control.

Unlike many lakes, composition of the healthy ecosystem in the ELA was well documented. That enabled scientists like David Schindler, then an ELA senior scientist and now emeritus professor at the University of Alberta, Canada, to add acid experimentally to one lake and see how the ecosystem responded. ELA scientists would protectively suit up like Darth Vader, make a sulphuric acid solution and use the boat propeller to mix the cocktail across one of the lakes.

Over seven years beginning in 1976, they lowered the pH of one lake, number 223, from 6.8 (close to neutral) to 5.0 (slightly acidic). Lab studies had suggested a pH of 5.0 would not harm fish. But in the lake 223 experiment, long before it reached 5.0, it did. By the time the pH reached 5.6, most of the lake trout’s preferred food – tiny organisms that require calcium to form exoskeletons – had died as acidified waters dissolved their protective coats.

“Lake trout stopped reproducing not because they were toxified by the acid, but because they were starving to death,” says Schindler.

Freshwater microbiologist Carol Kelly arrived at ELA in 1978 just as acid rain experiments got underway. She became curious about a particular puzzle the lake acidification experiments had stumbled on. Her colleagues had carefully calculated the quantity of acid needed to drop lake 223’s pH to 5.0 – a simple calculation a high-school student could do. But out in the lake it became clear that their calculations were way out of whack.

“I had given the crew orders to take the lake down to a given pH and then add enough acid to hold it there,” says Schindler. Part way through the season, the crew reported that they were running out of acid. Acidifying the lake took way more than they thought, says Kelly. “The question became, where is it going?” she says.

Kelly and colleagues set to work to find out, and discovered that alkali-producing microbes were capable of buffering some of the acidity, helping the lake chemistry to recover. That acid could be neutralised by bacteria living in every lake was a controversial finding at the time.

“People didn’t believe it,” Kelly says. But she continued to find out just how much acid microbes could neutralise, travelling elsewhere in Canada, the US and Norway to lakes that had been acidified atmospherically, to test this natural recovery ability. The discovery that acid-neutralising bugs exist in the sediment in lots of lakes, not just at the ELA, suggested that lakes could recover if the pollution causing the acid rain were eliminated.

Doubt and denial

Compelling photographs of starving fish from lake 223, combined with efforts by environmental groups like the Canadian Coalition on Acid Rain, helped persuade policymakers – eventually – to legislate more rigorous air quality standards.

But acid rain research at ELA almost didn’t happen at all. Founded to address the issue of excess nutrients contaminating lakes, work that had already drawn far-reaching conclusions by the early 1970s, Canada’s federal government was poised to pull the plug on the research station. At a presentation to federal fisheries officials, Schindler says that despite considerable evidence from the US, one official accused him of inventing the idea of acid rain just to save the ELA.

Scientists began pinpointing culprits and journalists covered the problem through the 1970s and 1980s, but some people working in industry were doing their best to obfuscate, sow doubt and delay action.

“There were lots of deniers of acid rain,” says Likens. At the time, Likens remembers giving public lectures on the topic. On occasion someone would stand up, rudely interrupt him, and say they didn’t believe in acid rain. “I would often respond by saying, ‘Well, have you ever collected a sample of rain and analysed it?’ They would say ‘No’ and I would say, ‘Well try it some time.’”

Like with climate change, says Likens, there were many big, powerful, wealthy people involved with vested interests. From its discovery in 1963 to passage of the Clean Air Act in 1990, legislative action on acid rain took 27 years.

Over that time, many a cross-border argument erupted. “The first international altercation over acid rain was the US accusing Canada of acidifying lakes in the boundary waters,” says Schindler. The squabble was over a small coal-burning power plant in Atikokan, Ontario, that US representatives claimed was sending acid rain south of the border. Schindler attended a meeting in Minneapolis, Minnesota, along with other Canadian scientists and their US counterparts.

“When all the data were on the table, it was clear that the little bit of sulphur from Atikokan was inconsequential to boundary waters,” Schindler says. At the same meeting, scientists examined net international flows of emissions. It became obvious, says Schindler, that the US, particularly the Ohio Valley and industrial areas of Pennsylvania and New England, were producing more than half the acid rain that collected in Canadian lakes.

The blame game continued, and acid rain “was at one time the number one Canada-US bilateral issue”, said Adèle Hurley in a speech reflecting on decades of work with the Canadian Coalition on Acid Rain, which she co-founded in 1981. The coalition was eventually disbanded following amendments to the US Clean Air Act in November 1990, establishment of the Acid Rain Program, and parallel action on the Canadian side.

Lessons from the lakes

A half-century after those early experiments, lake 223 in the ELA is no longer acidic, the acid-eating microbes having done their job. Lake chemistry has returned to its pre-experimental state. Biological recovery, however, has lagged behind. Freshwater opossum shrimp are found in healthy numbers in untouched control lakes. But in 223, they are still missing. So, Desjardins and others are investigating whether reintroductions of the opossum shrimp – 10,000 painstakingly counted at a time – might jumpstart biological recovery of the ecosystem.

Early signs look positive. Remote operated underwater vehicles searching for evidence of these mini-monsters of the deep have spotted just two Mysis shrimp swimming freely in lakes thus far, but it suggests that all that midnight catching and counting in the dark is not in vain – these tiny missing links in the ecosystem eroded by acid rain may be coming back. 

Broader recovery, in lakes across North America, happened because acid rain was tackled at its source.

Compared with 1990 levels, sulphate ions in the atmosphere have dropped considerably, reduced to almost negligible levels at former hotspots. But the problem has not disappeared altogether. Nitrates from sources like agriculturally emitted ammonia released from fertilisers and livestock feed remain a contributor to nitric acid precipitation. And there is concern that acid rain – from both sulphur and nitrogen – is an increasing problem in Asia.

There are no simple solutions to complex environmental problems. But are there parallels between efforts to curb acid rain and strategies for action on climate change? Schindler does see similarities in the procrastination tactics employed by industry. “Seed enough doubt, and pay for enough political campaigns, and you can delay action,” he says. “That sounds pretty crass but if you look closely, that’s how most environmental problems are addressed, and climate is no exception.”

Despite this, emissions reductions have been a huge success story in tackling acid rain, says Likens. But further reductions, especially on nitrogen oxides, are needed. The current US president is proposing to cut back regulations on emissions. If this happens, says Likens, recovering lakes in places like the Adirondack Mountains in north eastern New York would be particularly vulnerable, their acid-neutralising capacity already weakened.

Tackling acid rain in North America required actions in two neighbouring countries. But for climate change, the challenge is broader and solutions must be global. Nevertheless, the two issues do share similarities. Both, says Hurley, require cutting-edge science, media coverage and finding common ground, building coalitions between opposing parties.

In the fight Hurley helped to lead against acid rain, this meant talking to coal workers at sportsmen’s shows, engaging them in conversations about clean water for fishing salmon, and going for walks in war cemeteries where acidity was ruining the limestone of gravestones.

Though aspects of its legacy remain, solutions to the acid rain problem moved forward, in North America at least, because it became a non-partisan issue. Hurley reflects that “a broad spectrum of people came to believe that it was important to protect natural resources – our forests, our northern lakes and the fish they contain – resources that belong to everyone”.

If anything can be learned from the acid rain story, it’s that the same breadth of support and dismantling of partisanship is necessary for protecting the Earth’s climate.

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• v.49(4); 2020 Apr

Acid rain and air pollution: 50 years of progress in environmental science and policy

Peringe grennfelt.

1 IVL Swedish Environmental Research Institute, PO Box 53021, 40014 Gothenburg, Sweden

Anna Engleryd

2 Swedish Environmental Protection Agency, Virkesvägen 2F, 10648 Stockholm, Sweden

Martin Forsius

3 Finnish Environment Institute, Latokartanonkaari 11, 00790 Helsinki, Finland

Øystein Hov

4 The Norwegian Meteorological Institute, P.O. Box 43, Blindern, 0313 Oslo, Norway

Henning Rodhe

5 Department of Meteorology, Stockholm University, 10691 Stockholm, Sweden

Ellis Cowling

6 Department of Forestry and Environmental Resources, NC State University, 5211 Glenhope Court, Cary, NC 27511 USA

Because of its serious large-scale effects on ecosystems and its transboundary nature, acid rain received for a few decades at the end of the last century wide scientific and public interest, leading to coordinated policy actions in Europe and North America. Through these actions, in particular those under the UNECE Convention on Long-range Transboundary Air Pollution, air emissions were substantially reduced, and ecosystem impacts decreased. Widespread scientific research, long-term monitoring, and integrated assessment modelling formed the basis for the policy agreements. In this paper, which is based on an international symposium organised to commemorate 50 years of successful integration of air pollution research and policy, we briefly describe the scientific findings that provided the foundation for the policy development. We also discuss important characteristics of the science–policy interactions, such as the critical loads concept and the large-scale ecosystem field studies. Finally, acid rain and air pollution are set in the context of future societal developments and needs, e.g. the UN’s Sustainable Development Goals. We also highlight the need to maintain and develop supporting scientific infrastructures.

Introduction

Acid rain was one of the most important environmental issues during the last decades of the twentieth century. It became a game changer both scientifically and policy-wise. For some time, particularly during the 1980s, acid rain was by many considered to be one of the largest environmental threats of the time. Observations of fish extinction in Scandinavian surface waters and forest dieback on the European Continent were top stories in the news media. Even in North America acid rain received large public and policy attention.

During the cold war, with almost no contacts between East and West, acid rain broke the ice and formed an opening for scientific and political collaboration, resulting in a treaty under the United Nations’ Economic Commission for Europe (UNECE), the Convention on Long-range Transboundary Air Pollution (often mentioned as CLRTAP but in this paper we call it the Air Convention) signed in 1979. Eight protocols have been signed under the Air Convention committing parties to take far-reaching actions, not only with respect to acid rain but also with respect to several other air pollution problems (Table  1 ). Emissions of all key air pollutants have been reduced significantly and for the most important acidifying compound, sulphur dioxide, emissions in Europe have decreased by 80% or more since the peaks around 1980–1990 (Fig.  1 ).

Table 1

The Convention on Long-Range Transboundary Air Pollution and Its Protocols

European emissions of sulphur dioxide (SO 2 —black), nitrogen oxides (NO x , calculated as NO 2 —green) and ammonia (NH 3 —blue) 1880–2020 (updated from Fig.  2 in Schöpp et al. 2003 )

In this paper, we present and discuss how the acid rain problem became a key environmental issue among industrial countries from the late 1960s and the following decades (Fig.  2 ). We view the problem from a science-to-policy interaction perspective, based on a Symposium in Stockholm in the autumn 2017 organised to manifest 50 years of international air pollution science and policy development. The Symposium involved both a testimony from a number of those involved in science and policy during the first decades of the history but also a discussion of what we have learned and how the experience can be used in the future. Further information about the symposium and its outcome can be found at http://acidrain50years.ivl.se .

The timeline of science and policy interactions in Europe and North America 1967–2018. (updated from Driscoll et al. 2012). Abbreviations not occurring in text. NAAQS: National Ambient Air Quality Standards under the US Clean Air Act; CCAA: Canadian Clean Air Act; RADM: Regional Atmospheric Deposition Model; MAGIC Model of Acidification of Groundwater in Catchments. It should be mentioned that Canada and US are both parties to the Air Convention and they have also signed and ratified most of its protocols

Our historical review will be limited to some of the issues brought up at the Symposium. For more information on the early history see Cowling ( 1982 ). A comprehensive description of the acid rain history has recently been published by Rothschild ( 2018 ). The history of the first 30 years of the science–policy interactions under the Air Convention is also described in Sliggers and Kakebeeke ( 2004 ).

Short historical review

The discovery and the early acid rain history.

In a deliberatively provocative article in the Swedish newspaper Dagens Nyheter in October 1967, entitled “An Insidious Chemical Warfare Among the Nations of Europe”, the Swedish scientist Svante Odén (Fig.  3 ) described a new and threatening environmental problem—Acid Rain. He pointed to the significant decrease in pH of rainwater and surface waters that had occurred over the previous decade and linked it to the large and increasing emissions of sulphur dioxide in Europe.

Svante Odén around 1970 (photo Ellis B. Cowling)

The discovery received immediate attention by the Swedish government and, a few weeks after Odén’s article, the minister of industry presented the issue at the Organisation for Economic Cooperation and Development (OECD), but it did not receive any political attention at that time. The issue was also brought up in OECD’s Air Pollution Management Committee by the Swedish delegate Göran Persson. Also, here the message was met by scepticism and the common opinion among the members in the committee was that sulphur dioxide was a local problem, which easily could be solved by tall stacks. It was not until Persson felt he was going to “loose the case” he “played his last card” and pointed to the observations of intercontinental transport of radioactivity from the Chinese nuclear bomb experiments. The opinion then changed and the meeting agreed that acid rain might be an issue to look into. From now on, OECD and the western world realised that air pollution might be a problem of international political dimensions.

Odén’s discoveries were to a large extent based on the regional precipitation networks that were running in Sweden and Europe. In 1947, the Swedish scientist Hans Egnér set up a Swedish network to investigate the importance of atmospheric deposition for the fertilisation of crops. In 1954, the network was expanded forming the European Air Chemistry Network (EACN) through initiatives by Egnér, Carl Gustav Rossby, and Erik Eriksson (Egnér and Eriksson 1955 ; see also Engardt et al. 2017 ). Data from these networks together with a Scandinavian surface water network set up by Odén in 1961 formed the basis for Odén’s observations on the ongoing acidification (Odén 1968 ).

Acid rain and many of its ecological effects were, however, recognised long before 1967–1968. In fact, many features of the acid rain phenomenon were first discovered by an English chemist, Robert Angus Smith, in the middle of the nineteenth century! In 1852, Smith published a detailed report on the chemistry of rain in and around the city of Manchester, England. Twenty years later, in a very detailed book titled “Air and Rain: The Beginnings of a Chemical Climatology”, Smith first used the term “acid rain” and enunciated many of the principal ideas that are part of our present understanding of this phenomenon (Smith 1872 ). Unfortunately, however, Smith’s pioneering book was substantially ignored by nearly every subsequent investigator.

In Norway salmon catches decreased substantially in the early 1900s and in 1927, Professor Knut Dahl hypothesised that acidification of surface waters could be a factor of importance for the extinction of fish. Later Alf Dannevig assumed that “The acidity of a lake is dependent on the acidity of the rainwater and the contributions from the soil” (Dannevig 1959 ).

Based on detailed field observations and experimental studies both in England and in Canada, beginning in 1955 and continuing through 1963, Eville Gorham and his colleagues built a significant foundation for contemporary understanding of the causes of acid precipitation and its impacts on aquatic ecosystems, agricultural crops, soils, and even human health (Gorham 1981 ; Cowling 1982 ). Thus, Gorham and his colleagues as well as Dahl and Dannevig had discovered major aspects of the causes of contemporary changes in the chemistry of atmospheric emissions and deposition and their effects on aquatic ecosystems.

But these pioneering contributions, like those of Smith a century earlier, were not generally recognised—neither by scientists nor by society in general. Gorham’s researches, like those of Smith a century before, were met by what Gorham himself acknowledged as a “thundering silence”, not only by the scientific community, but also by the public at large.

It was not until 1967 and 1968 when Svante Oden published both his deliberatively provocative article in Dagens Nyheter and his carefully documented Ecological Committee Report (Odén 1968 ) that the acid rain problem was brought to both public and scientific considerations. The report included a huge body of scientific and policy-relevant evidence that long-distance transport and deposition of acidifying pollutants were causing significant environmental and ecological impacts, even in countries far away from pollutant-emitting source areas in other countries.

The Swedish case study and the OECD project

Two years after Odén’s article, the Swedish government decided to prepare a “case study” as a contribution to the UN Conference on the Human–Environment in Stockholm 1972 (Royal Ministry of Foreign Affairs and Royal Ministry of Agriculture 1972 ). Bert Bolin at the Stockholm University was appointed chair of the study, which included Svante Odén, Henning Rodhe, and Lennart Granat as authors. The report included a broad environmental assessment of the sulphur emission problem including sources, atmospheric and surface water chemistry, and effects on ecosystems and materials. Finally, it also included scenarios and estimated costs for environmental damage and control; in fact it was probably the first full systems analysis of an environmental problem.

In the report, a first estimate was made of the relative contributions of domestic and foreign emissions to the sulphur deposition in Sweden (Rodhe 1972 ). Estimates were also made of the effects of sulphur emissions on excess mortality and showed that 50% of the Swedish lakes and rivers would reach a critical pH level within 50 years (assuming continuation of present emission trends). Even if some aspects of the report received criticism, the overall case study was well received by the UN conference and in its final report (see http://www.un-documents.net/aconf48-14r1.pdf ) regional air pollution was explicitly mentioned (§85) with a citation of the Swedish study.

The Swedish initiative in the OECD resulted in a collaborative project to investigate the nature and magnitude of the transboundary transport of emitted sulphur dioxide over Western Europe, in which 11 countries participated. To initiate the project, a Nordic organisation on scientific research, Nordforsk, was asked to plan and develop methodologies for the investigation. Scientists and institutions from Norway, Sweden, Denmark, and Finland established an expert group in April 1970, which became central for the development and implementation of the OECD project. The Norwegian Institute for Air Research (NILU) offered through its director Brynulf Ottar to coordinate the project. The project included emission inventories, measurements of atmospheric concentrations, and deposition, together with model development and application for the assessment of the transport. A key part of the model calculations was to prepare the so-called “blame matrices”, through which the transport of pollutants between countries could be quantified.

The main conclusion from the OECD project, published in 1977, was that “Sulphur compounds do travel long distances in the atmosphere and the air quality in any European country is measurably affected by emissions from other European countries” (OECD 1977 ). Even if there still were hesitations about the magnitude of the transport, the common opinion was that transboundary transport of air pollution is an issue that needs collaboration across national borders. These conclusions paved the road for a pan-European scientific collaboration on air pollution, the European Monitoring and Evaluation Programme (EMEP) starting in 1977. The findings from the project also formed the basis for the Air Convention (Table  1 ). EMEP was already from the beginning included in the Convention as a key element, strongly contributing to the scientific credibility of the policy work.

Threats to forests boosted the interest

In 1980, the German scientist Bernhard Ulrich warned that European forests were seriously threatened from atmospheric deposition of sulphur. From his long-term experiments in the Solling area, he concluded that the high deposition of atmospheric pollutants had seriously changed the soil chemistry (Ulrich et al. 1980 ). Ulrich pointed to the links between sulphur deposition and the release of inorganic aluminium. His findings became a policy issue not only in Germany but in Europe as a whole, and even in North America. The alarms—often exaggerated—went like a wildfire through media and changed many attitudes throughout Europe. Newspapers were filled with photos of dying forests, in particular from “The Black Triangle”, the border areas between Poland, East Germany, and Czechoslovakia, characterised by large combustion of brown coal with high sulphur content. Forest inventories showed crown thinning and other effects on forests, but it became difficult to finally determine that acid deposition was the (only) cause for the observed effects.

The increasing interest in regional air pollution also paved the way for the first international agreement on emission control under the Air Convention. As a start, countries with a large interest in taking actions formed a “club” under the Convention, aiming for a 30% reduction in emissions. This ambition then became the basis for the first emission reduction protocol, the Sulphur Protocol signed in 1985. While Germany and some other West European countries acted almost immediately on the alarms, the progress in emission control in Eastern Europe was very slow during the 1980s, even though several of these countries signed the protocol. In fact, substantial decrease in emissions did not take place in the East until after the break-down of the communist regimes and the industrial collapse around 1990.

Critical loads and advanced policies

One of the most well-known characteristics for the control of the acid rain problem is the concept of Critical Loads (Nilsson 1986 ; Nilsson and Grennfelt 1988 ). The Executive Body, the highest decision-making body of the Air Convention, decided in 1988 that new negotiations on the control of sulphur and nitrogen emissions should be based on critical loads, and all parties to the Convention were requested to prepare their own critical load maps. The Netherlands offered to take a lead and prepared mapping manuals and initiated an international network, which became crucial for the scientific and policy acceptance of the concept (Hettelingh et al. 1991 ; De Vries et al. 2015 ; Fig.  4 ). (The critical loads concept is further discussed later in the paper)

The outcome of emission control of SO2, NOx, and NH3 between 1990 and 2010 presented as maps on exceedance of critical loads of acidity. Such maps have played an important role for illustrating outcomes of future policies as well as of actions taken (from Maas and Grennfelt 2016 )

When critical loads became a basis for further protocols, Integrated Assessment Models (IAMs) offered a method to calculate how to achieve a prescribed ecosystem effect reduction in the most cost-effective way. A couple of different approaches were developed, but the model at the International Institute for Applied Systems Analysis (IIASA) became the official model on which the Second Sulphur Protocol signed in 1994 was agreed (Hordijk 1995 ).

When revising or developing a new protocol for nitrogen oxides the concept could, however, not be used in the same way as for sulphur and acid deposition, since the NO x emissions contributed to several effects and, in addition, a strategy would need to take additional compounds into account. Instead, a more advanced approach was suggested by which both several effects and several compounds could be considered simultaneously (Grennfelt et al. 1994 , Fig.  5 ). IIASA and other bodies under the Air Convention were asked to develop an integrated assessment model that fitted into a broader approach and a more comprehensive model was developed, which made it possible to simultaneously take into account the effects of acidic deposition, nitrogen deposition, and ozone—the so-called multi-pollutant, multi-effect approach. The calculations became the basis for the Gothenburg Protocol (GP) that was signed in 1999 (Amann et al. 1999 ). The GP and the parallel EU National Emissions Ceilings (NEC) Directive from 2001 outlined control measures for 2010 and beyond.

Links between sources and effects used as an illustration in the preparation of the Gothenburg Protocol. From Grennfelt et al. 1994

After 2000—Health effects and integration with other policies became main drivers

The basis for the GP was almost entirely ecosystem effects. Around 2000, however, public health effects from air pollution became increasingly important. Large epidemiological studies indicated that air pollution was a significant source of premature deaths and that particles were a main cause of the health effects (WHO 2018 ). When the European Commission started its work to revise the NEC directive, health effects became central and the Air Convention followed. Further studies have supported the role of air pollution for health effects and when the GP was finally revised in 2012, health effects dominated as a policy driver for the establishment of national emission ceilings, and for the first time particulate matter was included in an international protocol (Reis et al. 2012 ).

When considering further actions after signing the GP in 1999, it was realised that for some pollutants under the Air Convention, emission control needed to be considered over larger geographic scales than Europe and North America alone. Ozone was of particular importance, since long-term objectives in the form of critical levels and public health standards could not be reached without taking into account sources outside the areas considered so far. Future policies therefore needed to include the ozone precursors methane and to some extent carbon monoxide. A task force on Hemispheric Transport of Air Pollution (HTAP) was set up under the Convention in 2004, with a primary objective to quantify the intercontinental transport of pollutants. The outcome of its work clearly showed the importance of considering air pollution in a wider geographic perspective than had been done so far (Dentener et al. 2010 ).

Climate change has for more than a decade become an issue of increasing interest for air pollution science and policy. In many cases, the emission sources are the same and there are obvious co-benefits (and some trade-offs) in handling them together. One aspect that has received large interest is the option to decrease short-term temperature increase through control measures directed towards atmospheric pollutants that also contribute to the warming of the atmosphere, in particular black carbon and methane (for methane both by itself but also as a tropospheric ozone precursor) (Ramanathan et al. 2001 ). Compounds contributing to both air pollution effects and to the radiation balance in the atmosphere have been named Short Lived Climate Pollutants (SLCPs). SLCPs thus also include compounds that are cooling the atmosphere, i.e. small secondary aerosols, e.g. sulphate particles. Recent research has focused on a better understanding of these compounds’ contribution to both air pollution and climate as well as on opportunities for selective control of these compounds (e.g. Sand et al. 2016 ).

Reactive nitrogen species are another group of compounds that has received increased attention after the turn of the century. Around 2006 several initiatives were taken in Europe, including a special task force on Reactive Nitrogen under the Air Convention, a large-scale EU project on nitrogen, and the preparation of a European Nitrogen Assessment (Sutton et al. 2011 ). Here nitrogen was considered both as a traditional atmospheric pollutant and within a societal and industrial context. A cascade perspective, where one fixed nitrogen molecule could contribute to a series of effects before it returns to molecular nitrogen again, was introduced (Galloway et al. 2003 ). The studies have pointed to the importance of the agricultural sector for the intensification of reactive nitrogen cycling, determined by food production mechanisms and dietary choices.

North America

In North America, the acid rain problem developed to a large extent in parallel with the situation in Europe. Lake acidification became already from the beginning a main driver, and monitoring programmes were set up both in the United States and Canada (Driscoll et al. 2010 ). The US National Atmospheric Deposition programme (NADP) started in 1976 and is still running. Both countries have taken part in the Air Convention activities and have signed most of the protocols and achieved decreases in SO 2 emissions of the order of 80% between 1980 and 2015. The US has however taken a different approach with respect to policy in comparison to Europe. Instead of developing a strategy based on integrated assessment modelling, it was decided to establish an emissions trading programme for the large electric generation sources under the Clean Air Act (See also UNECE 2016 ).

Characteristics of the science–policy interactions

In this section we will, from a science–policy perspective, briefly discuss some characteristics of the history of acid rain and transboundary air pollution that have become central for the international collaboration, not only on air pollution but also for international environmental collaboration in general. We will bring up monitoring, modelling, and data collection (including field experiments and long-term studies carried out in order to understand and quantify effects to ecosystems), development of bridging concepts that have served the implementation of strategies, and finally the dynamics in the science–policy interactions.

Monitoring, modelling, and data collection

Monitoring of atmospheric concentrations, deposition, and ecosystem effects has been a key for understanding the causes, impact, and trends in acid rain, both in Europe and North America and later in other geographic areas (Table  2 ). The original EMEP network has since the start over 40 years ago formed a broad atmospheric monitoring system. The originally established simple monitoring stations have over time been complemented with more advanced monitoring, and some stations are today advanced atmospheric chemistry platforms with continuous collection of a multitude of atmospheric parameters (Fig.  6 ). The EMEP database is nowadays widely used for a variety of scientific purposes including computation of long-term trends, exposure estimates, and as a basis for modelling. EMEP has also become a model for monitoring networks related to other geographical regions, conventions, and purposes. One example is the acid deposition monitoring network in East Asia (EANET). It is obvious that having a qualified centre for data collection and storage, standardisation, and intercalibration of methods has served the international policy system extremely well. Its open nature is part of the success. The financial support to EMEP, regulated through a separate protocol, has been fundamental for the development and progress of the monitoring activities.

Table 2

Long-term monitoring activities in relation to acid rain and other pollutants

Atmospheric monitoring stations have been of importance for understanding the long-range transport and chemical conversions of atmospheric pollutants. Pallas air pollution background station in Northern Finland (Photo Martin Forsius)

Monitoring of air pollution effects in a systematic way under the Air Convention started a few years later than EMEP and was organised through so-called International Cooperative Programmes (ICPs). Separate programmes were set up for forests, waters, vegetation (primarily ozone), materials, and integrated monitoring. A separate ICP was set up for developing critical load methodologies and coordinating European-scale mapping activities (ICP Modelling and Mapping). The ICPs are of great importance for general understanding of the magnitude and geographical distribution of the effects and for showing how decreases in emissions have led to beneficial conditions in ecosystems and decreased material corrosion (Maas and Grennfelt 2016 ). Ecosystem monitoring is also important for the development and verification of ecosystem models. Since their start, the responsibility for the ICPs has been taken by different parties of the Air Convention (Table  2 ). The distributed responsibility has been of large importance for the establishment of networks of monitoring sites among the Convention parties, but the system has not had a stable financial support in the same way as for EMEP. This has resulted in the lack of a common source for easily accessible data or adequate resources for standardisation and intercalibration.

Monitoring and other data collection (i.e. emissions and critical loads) under the Air Convention are responsibilities of every country, and data are then used for the assessments on the Convention level as well as for the development of EU air pollution policies. The bottom-up process in data collection is important for the development of national expertise and, not the least, for the establishment of national policies. In this way, direct communication links between the science and the policy levels within countries have evolved.

Numerical modelling of atmospheric pollution is also a long-term commitment under EMEP. The atmospheric chemistry models are necessary for the understanding of the nature of transboundary transport but also to make budget estimates of the exchange of pollutants over Europe and North America, and later on a hemispheric scale. The Meteorological Synthesizing Centre West at the Norwegian Meteorological Institute together with the Eastern Centre in Moscow took the lead in this work. In addition to calculating transboundary fluxes, the centres are important for coordinating modelling efforts done by other groups, forming a basis for scrutinising models and support further modelling.

Field experiments and long-term studies—a way to understand processes and trends, and to visualise the problems

Some of the most important and reliable findings regarding acid rain and its effects on ecosystems emanate from long-term field experiments. These experiments, which are known from the sites where they are run, include Hubbard Brook (US), Solling (Germany), Risdalsheia (Norway) and Lake Gårdsjön (Sweden) (Fig.  7 ). The studies there have shown how acid deposition and the impact of other air pollutants have changed the ecosystems, but also how ecosystems respond to decreased emissions (e.g. Wright et al. 1988 ; Likens et al. 1996 ). A central feature in all these field experiments was the establishment of ion budgets, from which the chemical effects on acid deposition can be analysed and understood (Reuss et al. 1987 ).

Field experiments have played an important role for the overall understanding of the interactions between atmospheric deposition and ecosystem effects. The photo illustrates the covered catchment experiment to study the recovery of ecosystems at reduced emissions in Risdalsheia Norway (Photo NIVA)

In the intense research period during the 1970s and 1980s, a number of large-scale research programmes and experiments of temporary nature were set up, some of them in connection with the above-mentioned sites. The first research programme of some magnitude was the Norwegian programme “Acid precipitation—effects on forest and fish” (SNSF), which run between 1972 and 1980 (Overrein et al. 1981 ). At that time the scientific understanding was limited, and the programme received a lot of attention. The results were important for the general acceptance that long-distance transport of sulphur caused acidification of surface waters, with a serious die-off of fresh water fish populations (salmon and trout) as a main consequence. On the other hand, the studies on Norwegian forests did not give any significant evidence for acid rain effects. The SNSF project was a joint effort across disciplinary and organisational boundaries, with scientists mainly from the research institute sectors outside of traditional academia. This project served as a model for later research programmes and provided educational opportunities for a new generation of scientists working together on all aspects of the acid rain issue—emissions and their control, atmospheric transport and deposition, impact on ecosystems, health and materials, and finally development of pollutant-control policies.

The long-term field experiments served another important task. The sites became exhibition platforms, at which policymakers, experts, scientific journalists, and leaders of non-governmental organisations (NGOs) and others can be informed about the problem directly on site. During the most intense period in the 1980s and early 1990s, politicians and industry leaders, often directly involved in decisions on the highest levels, visited many of these experimental sites. For example, US congress members travelled across Europe to see and understand the issue in preparation for the 1990 amendment of the Clean Air Act.

Bridging concepts and approaches

Concepts developed, such as critical loads and similar approaches, formed links between science and policy, and were essential for the understanding and scientific legitimacy of the policy measures. These concepts also formed a basis for priority setting in agreements under the Convention and the EU, but also to some extent for national policies. Even “acid rain” can be considered as a bridging concept. While the acidity from sulphur and nitrogen compounds is threatening ecosystems through a chemical change, the expression also gives the impression of a threat to the life-giving rain, a fundamental necessity for life on Earth.

The quantification of transboundary fluxes was very important politically. The establishment of national budgets and so-called blame matrices formed the first bridging concept. The development of mathematical models to calculate source–receptor relations was a scientific challenge but when the annual tables were prepared showing the interdependence between countries with respect to atmospheric emissions and deposition, they served as an important basis for the need for common action. Anton Eliassen, the leader of the modelling centre at the EMEP Meteorological Synthesising Centre West (MSC-W) during many years (the Eastern center is in Moscow—MSC-E), was key to this development as well as for the communication of the results to policymakers.

As earlier mentioned, critical loads played an outstanding role for the development of the more advanced strategies leading to the Second Sulphur Protocol and the GP. Critical loads formed a successful link between science and policy that became crucial for the negotiations and agreements. The concept, first discussed in 1982, was taken from the original idea to application quite quickly during the 1980s. The Swedish expert Jan Nilsson was a key leader for the success of the concept, and the Nordic Council of Ministers played a unique role for forming the links between science and policy. Through a series of workshops involving both key scientists and key policymakers, the concept gained the legitimacy on which policies were developed. According to Jan Nilsson, it all started with requests from both industry and negotiators to have a sounder base for emission control, something that could express the long-term objectives for emission control policies. The concept was first met by scepticism, not least from scientists, but after a couple of workshops, the interest turned around and the concept became widely accepted (Nilsson 1986 ; Nilsson and Grennfelt 1988 ). When critical loads were included in the plans for the next rounds of the sulphur and nitrogen protocols in 1988, it changed the way the Air Convention operated.

The application of the critical loads concept has encouraged intense research over several decades where the main objective has been to find simple chemical parameters that can mimic the (often biological) real effects or effect risks. For lake acidification, where the effects of dissolved aluminium on fish often were chosen as the main biological effect, the acidity of the water, mostly expressed as acid neutralising capacity (ANC), is used (e.g. Henriksen et al. 1989 ; Forsius et al. 2003 ; Posch et al. 2012 ). For forests, where the toxicity of aluminium to tree roots is considered as critical, the Al 3+ to Ca 2+ ratio in soil water has become the main effect parameter (Sverdrup et al. 1990 ; de Vries et al. 1994 ).

Integrated assessment modelling (IAM) also has been a bridging concept. The idea of applying systems analysis goes back to the work at IIASA in the beginning of 1980s. A conceptual model was formulated by Joseph Alcamo, Pekka Kauppi, and Maximilian Posch for the interactions between emissions, their control (including costs), and the effects on ecosystems (Alcamo et al. 1984 ). Their work of bringing together the scientific knowledge to a comprehensive systems analysis tool formed a new way of framing environmental policies. Under the leadership of Leen Hordijk, the new idea was introduced to and accepted by the policy side, which had asked for more targeted methods for policies than simple percentage decreases in amounts of emissions. IAMs as a policy-supporting concept was then taken further by Markus Amann, who led the development of the more advanced RAINS (later GAINS) models that were used as a basis for the GP and later agreements (Amann et al. 2011 ). From the strategies strictly directed at ecosystem effects, the approach is now widened to include health effects, local air pollution impact, climate policies, and reactive nitrogen.

All the bridging concepts are to varying degrees dependent on underlying models, assumptions, and simplifications. For these to be accepted among policymakers, it is important to keep transparency and confidence in the underlying data and to scientifically evaluate and scrutinise them. This is particularly important for the IAMs, which are the final step in a chain of inputs (Fig.  8 ). The models have often been criticised, not least from industry and other stakeholders that are questioning the priorities that result from the IAM calculations. IIASA, as a provider of the model calculations, has, however, been transparent, and countries and stakeholders have always had the option to re-check data and take this into account when developing their own negotiation positions.

The scientific support to regional air pollution policies consists today of a series of steps. The policy side may often only see the integrated assessment step and not realise that the legitimacy of the use of scientific support builds on an advanced system of underlying research and development

Forming science–policy credibility

In all interactions between science and policy, it becomes crucially important to maintain scientific credibility. The close involvement of scientists has been a signature of the Air Convention. Scientists have always had a role at the policy meetings, communicating results from basic scientific research over outcomes of monitoring and inventories to presenting options for control strategies. Scientists have in this way taken the responsibility to move scientific knowledge into the policy system and presenting results in a way that has been understandable and useful for the policy work. The role of the scientists has been as honest brokers , not that of issue advocates to follow the terminology of Pielke ( 2007 ). The leadership from the policy side and its sensitivity to changes in the underlying science and observations of new problems have also been important, and have resulted in repeated changes in the framings of the Air Convention to adapt to new situations: going from an initial framing around sulphur and acidification, through extension to eutrophication, human health, materials, crops, biological diversity, and finally to links to climate, urban air quality, and societal changes. A balanced interplay between the two communities has in this way been developed and maintained over time.

Another factor is the building of networks. The strong networks of scientists and policymakers pushed the politicians. The whole field of international diplomacy during these four decades of the Convention is built on incremental developments forming protocols of increasing capability to solve specific environmental issues by cutting emissions in a cost-effective way.

Future challenges

New approaches necessary.

International air pollution control is by many considered as a success story. However, the success is in many ways limited to Europe and North America and a few additional industrialised countries (including Japan and Australia), where emissions of sulphur dioxide, nitrogen oxides, VOCs, and some other compounds have been decreased significantly (Maas and Grennfelt 2016 ). But even in the areas, where air pollution has been a top priority for several decades, air pollution remains a problem. Ecosystem effects, which were the main reason for the establishment of the Convention, are to some extent reduced, but the acidification effects of historical emissions will remain for decades (Wright et al. 2005 ; Johnson et al. 2018 ) and the emissions of ammonia have so far only been reduced by 20–30% in Europe and even less in North America. Looking at health effects, it is difficult to talk about success, when hundreds of thousands of inhabitants on both continents are predicted to meet an earlier death due to air pollution.

But the problem is even larger and more urgent when looking outside the traditional industrialised world. The focus is today on the large urban regions in the countries that are facing rapid population growth and industrialisation. Although large efforts now are being made to decrease sulphur emissions in China—the world’s leading sulphur emitter—major challenges remain. In India and several other countries, sulphur emissions are still increasing. Estimates indicate that more than four million people die prematurely due to outdoor air pollution globally ( https://www.who.int/airpollution/ambient/health-impacts/en/ ). It is assumed that fine particles (PM2.5) are a main cause for the health effects. The new and great challenge is therefore to control air pollution in relation to health risks, in particular by decreasing exposure to the small particles.

There is, however, a risk that control measures will only to a limited extent focus on the right sources and the right measures. In Paris, several air pollution episodes with high concentrations of particles have occurred during recent years. At first, these episodes were considered to be caused essentially by local emissions. More thorough analysis has, however, shown that they were to a large extent caused by regional emissions and buildup of high concentrations over several days when urban emissions of oxides of nitrogen from traffic mix with ammonium emissions from surrounding agricultural areas to form particulate nitrate. Similar situations are also often encountered in urban regions in developing countries, e.g. by agricultural waste burning, and need to be considered. Air pollution problems are, as previously mentioned, also linked to intercontinental and hemispheric scales.

It is also obvious that the research communities within air pollution and climate change need to work more closely together. Health aspects are of importance both from air pollution and climate change perspectives, and heat waves carry poor air quality as winds are often very low and the atmospheric boundary layer stagnant. During heat waves, the soil and vegetation dry up and increase the likelihood of fires, which also can cause severe air pollution, as seen in wildfires around the world (e.g. California in 2018).

Despite the large progress in atmospheric and air pollution science, basic questions still need further investigations to develop the best policies. Such areas include a better understanding of health effects from air pollution, nitrogen effects to ecosystems, and air pollution interactions with climate through carbon storage in ecosystems and impacts on radiation balances. Modelling is a scientific area where much progress has been made and where increased computer power, as in climate change research, has allowed integration of atmospheric chemistry into the climate models formulated as Earth system models, coupling the atmosphere, ocean, the land surface, cryosphere, biogeochemical cycles, and human activities together. This has allowed studying air pollution and climate change simultaneously. The modelling approach can be further developed when observations are designed to map Earth system component boundaries to understand and quantify the flows and interactions between different compartments, including terrestrial and aquatic ecosystems. Air pollution should be an integrated part of such models. In this context, global-scale concepts such as “planetary boundaries” and “trajectories of the Earth system vs. planetary thresholds” have been developed (Rockström et al. 2009 ; Steffen et al. 2018 ).

Solutions are available; driving forces and investments are lacking

In 2016, the Air Convention launched a scientific report “Towards Cleaner Air”, in which the actual air pollution situation within the UNECE region was updated (Maas and Grennfelt 2016 ). The report also presented future challenges and ways forward to solve the air pollution problems. It also showed that solutions are available for most of the identified problems at affordable costs below the health and ecosystem benefits of the control actions.

Even if solutions are available, many parts of the world are facing large problems in implementing them. There are several reasons, but often there is a lack of knowledge and resources. This is particularly true in many developing countries. Another reason is the lack of political interest. Air pollution is still not of top priority among politicians, even if there is overwhelming evidence that air pollution is one of the most common causes of shortened life expectancies. Another reason may be that other interests (e.g., industry and agriculture) are forming strong lobbying forces delaying actions.

Air pollution is a problem that cannot be seen in isolation. Future policies need to take into account climate change and climate change policies. Whereas some air pollutants—in particular black carbon particles—contribute to warming, others, including sulphate particles, tend to cool the climate. A reduction in sulphur dioxide emissions, although highly desirable from health and ecosystems perspectives, will therefore contribute to warming. On the other hand, a reduction of black carbon will be a win–win solution. It is also important to see air pollution control in the perspective of sector policies, such as energy, agriculture, transportation, and urban planning in order to meet the challenges to decrease air pollution problems.

Internationally coordinated actions and infrastructures are keys for success

The perspective of international cooperation on air pollution is changing. Policy development is no longer limited to long-range transport in line with that developed under the Air Convention. The ranking of air pollution as a top ten cause of premature deaths in the world has given high priority to the issue within fora such as the WHO and UN Environment. Both organisations have adopted resolutions calling for actions (WHO 2015 ; UN Environment 2017 ). Additional initiatives are taken by other organisations, such as the World Meteorological Organisation (WMO), the Climate and Clean Air Coalition (CCAC), and the Arctic Monitoring and Assessment Programme (AMAP). WMO is particularly important as a global technical agency for weather and climate observations, research and services, and it is rapidly developing its regional and global capacities in Earth system observations, modelling, and predictions to the benefit of mitigating a range of environmental threats and for global use. The research is done in large programmes like Global Atmosphere Watch (GAW) and the World Weather Research Programme (WWRP). Even if the starting point and modes of action can be different, all initiatives are aiming for the same goal, cleaner air. It is also worth mentioning the initiative taken by the International Law Commission, under which a proposal for a Law for the Protection of the Atmosphere has been prepared ( http://legal.un.org/ilc/summaries/8_8.shtml ) but in the current international atmosphere there is a lack of political support to implement it. Our hope is that the situation will change soon—the initiative is too important to fail.

The UN has put forward a very strong agenda in order to reach the Sustainable Development Goals (SDGs), and air pollution is an integral part of several of the SGDs, like goal No 2: No Hunger, No 3: Good health and well-being, No 6: Clean Water, No 7: Affordable and clean energy, No 9: Industry, innovation and infrastructure, No 11: Sustainable cities and communities, No 13: Climate action, No 14: Life below water, No 15: Life on Land, No 16: Peace and Justice, and No 17: Partnerships for the Goals. The approach taken to develop multiple pollutant—multiple impacts protocols under the Air Convention can serve as important learning ground to meet the ambitions of many of the SDGs. Air pollution plays an integral role in the evolution of the food production and ecosystem services, the health of the population, the shape of the energy and transportation systems, and the availability of clean water. Climate change is a very significant common and cross-cutting factor.

The Air Convention has taken some steps in promoting air pollution on a wider scale. Due to its long history and well-developed structure, it has taken a role of making sure that international organisations having air pollution on its agenda are aware of each other and to invite to further collaboration and development. Initiatives are taken both within the formal Convention structure and through dedicated workshops (UNECE 2018 ; Engleryd and Grennfelt 2018 ). The approach developed under the Air Convention, which has proven successful in linking scientific evidence, monitoring, and integrated assessment modelling directed towards cost-effective solutions, may also serve as a working model for environmental problems in other fields.

These new international initiatives have a strong emphasis on policy development. The experience from the 50 years of international air pollution development is the value of well-defined scientific objectives and activities supporting policy. The increased interest from WHO and UN Environment is welcome and there are expectations of an active role from these organisations in combatting the situation in many parts of the world. However, for these organisations, air pollution is just one of several priority areas, and priorities may change. Further, none of these organisations are likely able to set up advanced infrastructures with respect to emission inventories, monitoring, and research. Here WMO needs to live up to its mission and capitalise on global research and development efforts and improve the global operational capability to observe, analyse, and forecast the development of the Earth system and its components, air pollution being an important part. This is in line with the WMO strategic plan and with fast growing capabilities in some countries and in global centres like The European Centre for Medium Range Weather Forecast (ECMWF). WMO, through GAW, is also developing a research-driven operational system (IG3IS) for top-down determination of greenhouse gas emissions, to complement the usual bottom-up-based inventories where emission factors and fuel consumption or production statistics form the basis for the emission estimates ( https://library.wmo.int/doc_num.php?explnum_id=4981 ). The Air Convention and the science support for the policy work there has been a model for the WMO ambitions on a global basis. However, current investments in these new capabilities are not enough to get the societal return they would offer.

Therefore, we see a need for developing long-lasting infrastructures that can continuously develop science-based control policy options, potentially as part of a wider network of global observatories for comprehensive monitoring of interactions between the planet’s surface and atmosphere (Kulmala 2018 ). Such a network should be able to support policies from local to the global levels. The challenge is how to organise and raise resources for scientific support on a wider scale. Financial institutions such as the World Bank and/or regional banks may step in and make sure that control measures and investments are made on a sound basis with respect to global air pollution.

There is also a need to mobilise new generations of scientists, scientists that are willing to cross boundaries and focus on thematic problems and to build legitimacy among policymakers (e.g. Bouma 2016 ). Today we have more developed and stronger political institutions to handle environmental problems, which may make it harder for scientists and individuals to influence and make a difference. It is also important to mobilise new generations of dedicated policymakers. Unfortunately, we also see that politicians often are questioning science and seeing science as just a special interest. Public awareness may be a key for forming stronger interests and put pressure on decision-makers. During the acid rain history, NGOs played an important role in driving the awareness at a wider scale than local or national actions and could be important for a more global movement towards cleaner air. We also see the need for a deeper responsibility not only from politicians but also from industry. The so-called “diesel gate” exposed the cynic view from parts of the industry to peoples’ health, which hopefully will not occur in the future. Instead we hope that it was an eye-opener and that industry instead can play a role as a forerunner and a positive power for a cleaner atmosphere.

Final remarks

The Acid Rain history taught us that when science, policy, industry, and the public worked together, the basis was formed for the successful control of, what was considered, one of the largest environmental problems towards the end of the last century. We learnt from experience that science-based policy advice worked well when the best available knowledge was provided, and used to understand the specific problems, generate, and evaluate the policy options and monitor the outcomes of policy implementation.

However, the world does not look the same today, and we cannot just apply the ways the international science community worked together then on today’s problems. But there are lessons to be learnt. Most important is the building of mutual trust between science advisers and policymakers, and that both communities are honest about their values and goals. In this way, a fruitful discussion around critical topics within society can be formed. The advice works best when it is guided by the ideal of co - creation of knowledge and policy options between scientists and policymakers (SAPEA 2019 ).

Acknowledgement

Open access funding provided by The Swedish Environmental Protection Agency. The Symposium could not have been arranged and this paper written without financial support from the Nordic Council of Ministers, the Swedish Environmental Protection Agency, the Mistra Foundation, and other organisations and institutes in the Nordic countries. We are also grateful to all participants of the Symposium and their contributions with background material for this paper. We also thank the two anonymous reviewers of the manuscript. Their comments greatly improved the quality of this paper.

Biographies

is a former Scientific Director at the Swedish Environmental Research Institute IVL. His main scientific activities include transboundary air pollution and environmental science–policy interactions.

is a Senior Policy Advisor at the Swedish Environmental Protection Agency. For the last 15 years, she has been a lead negotiator on air pollution for the Swedish Government in several international fora. Since 2014, she is the chair of the Executive Body to the UNECE convention on long-range transboundary air pollution. She has a background in energy efficiency and agronomy.

is a Research Professor at the Finnish Environment Institute SYKE. His research interests include impacts of air pollutants and climate change on biogeochemical processes.

is the Secretary General of The Norwegian Academy of Science and Letters and adviser to the Director General of the Norwegian Meteorological Institute. His research interests include atmospheric chemistry and earth system modelling.

is a Professor Emeritus at the Department of Meteorology and Bolin Centre for Climate Research at Stockholm University. His research interest includes atmospheric transport processes and climate impact of aerosol particles.

is University Distinguished Professor At-Large Emeritus at North Carolina State University in Raleigh, North Carolina. He was founding leader for the US National Atmospheric Deposition Program (NADP), which played a crucial role for the development of acid rain research and policy in North America from the 1970s and onwards.

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Contributor Information

Peringe Grennfelt, Email: [email protected] .

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Ellis Cowling, Email: ude.uscn@gnilwoc_sille .

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Acid Rain and Our Ecosystem

More than 150 years after acid rain was first identified, scientists now see success in recovery from its damaging effects

Cassandra Willyard

Geologist Rich April climbs the small hill behind Colgate University and makes his way into the cemetery. He stops before a white marble pillar erected in 1852. The inscription is nearly illegible. Over time, any stone exposed to the elements will weather, April explains, but this marble has weathered unnaturally fast. The culprit? Acid rain.

April pulls a vial of acid from his pocket to demonstrate. He unscrews the cap and lets a few drops leak onto the stone, where they fizz and bubble. The rain that fell throughout the Northeast in the latter half of the 20th century wasn’t as acidic as the liquid in April’s vial, but the principle is the same. Acid eats marble. Given enough time, it can erase even words meant to last an eternity.

The effects of acid rain extend far beyond graveyards. Acid rain destroyed fish populations in lakes and streams, harmed fragile soils and damaged millions of acres of forest worldwide.

These far-reaching effects illustrate the profound impact air pollution can have on the land. But the story of acid rain is also a tale of how understanding air pollution can lead to solutions. Due to overwhelming scientific evidence linking power plant emissions to acid rain and acid rain to the death of lakes, new regulations have dramatically cut emissions and cleaned up the rain that falls on the United States.

The term ‘acid rain’ was coined in the mid-1800s, when Robert Angus Smith, a Scottish chemist working in London, noticed that rain tended to be more acidic in areas with more air pollution and that buildings crumble faster in areas where coal is burned. But it took another century for scientists to realize that acid rain was a widespread environmental problem. Scandinavian scientists began to document acidic damage to lakes and streams in the 1950s. In 1963, Gene Likens, then at Dartmouth, and colleagues began collecting and testing the pH of rainwater in New Hampshire’s White Mountains as part of an ecosystem study. They were surprised to find that it was quite acidic, but they didn’t have much basis for comparison; at that time, scientists weren’t regularly measuring the pH of rainwater.

Likens took a job at Cornell a few years later and set up instruments to collect rainwater in the Finger Lakes region and soon observed that the rain in New York was roughly as acidic as rain in New Hampshire. “That was the first clue that we had that this might be some kind of a regional phenomenon,” he says. But neither Likens nor his colleagues had a clear idea what the cause might be.

Likens won a fellowship that took him to Sweden in 1969, a serendipitous event, he says, because he met Svante Odén, a scientist at Uppsala University who had observed the same trends in Sweden that Likens had been observing in the Northeastern United States. Odén had his finger on a potential cause. “He was trying to build a case that [acid rain] might be due to emissions coming from the more industrialized areas of Europe,” Likens recalls.

Likens and his colleagues traced the emissions from coal-fired power plants and examined satellite and aircraft data, and they found a similar long-distance link. “Sure enough, the emissions were coming primarily from Midwestern states like Indiana, Ohio, Illinois and Kentucky,” Likens recalls. “They were making their way literally thousands of kilometers to New England and southeastern Canada and coming back down as acids.”

He reported his findings in Science in 1974, and the story was immediately picked up by newspapers. The phone didn’t stop ringing for months, Likens recalls. “It was that media exposure that really put acid rain on the map in North America.”

Acid rain occurs, Likens and Odén and other scientists realized, when sulfur dioxide and nitrogen oxide enter the atmosphere and react with water to form sulfuric and nitric acids. Natural sources of these gases exist—volcanoes, for instance, belch out sulfur dioxide—but the vast majority comes from the burning of fossil fuels, especially by coal-fired power plants. The tall smokestacks allow pollution to travel long distances. According to studies conducted by Likens and his colleagues, normal rainwater has a pH of 5.2. During the 1970s and 1980s, when acid rain was at its worst, scientists recorded pH levels as low as 2.1, roughly 1,000 times more acidic.

Acid rain affected many parts of the United States, but the Northeast suffered the most ecological damage. The Adirondack Mountains proved especially susceptible. Many soils contain calcium carbonate or other minerals that can neutralize acid rain before it seeps into lakes and streams. “Unfortunately the Adirondacks have almost none,” April says. As a result, lakes and streams quickly became acidic, killing fish and other aquatic animals.

In the late 1970s, researchers surveyed 217 lakes above 2,000 feet in the Adirondacks and found that 51 percent were highly acidic. The news was so grim that scientists began attempting to breed more acid-tolerant strains of trout. One New York State employee compared the area to Death Valley. A decade later, a larger study that included 849 lakes higher than 1,000 feet found that 55 percent were either completely devoid of life or on the brink of collapse.

As the scientific evidence linking acid rain to power plant emissions and ecological damage mounted, battles erupted among industry, scientists and environmentalists. “The 1980s is a period I call the ‘acid rain wars,’” Likens says. “There was huge rancorous nasty controversy.” Environmentalists from Greenpeace climbed power plant smokestacks and hung banners in protest; scientists testified before Congress about the link between emissions and acid rain, the severity of the effects, and whether proposed legislation would have an impact; and the power industry questioned the science and argued that regulations would drive electricity rates sky high.

Congress passed several amendments to the Clean Air Act in 1990 that cut emissions of sulfur dioxide through a cap-and-trade scheme. The goal was a 50 percent reduction in sulfur dioxide emissions from 1980 levels. That goal was achieved in 2008, two years before the deadline, which was set for 2010. Sulfur dioxide emissions fell from 17.3 million tons in 1980 to 7.6 million tons in 2008, less than the 8.95 million tons required by 2010.

The effect has been remarkable. Doug Burns, a scientist at the U.S. Geological Survey in Troy, New York, who directs the National Acid Precipitation Assessment Program, says the rain falling in the Northeast today is about half as acidic as it was in the early 1980s. Consequently, surface waters have become less acidic and fragile ecosystems are beginning to recover.

In many places, however, recovery has been painfully slow. Scientists now know that acid rain not only acidified lakes and streams, it also leached calcium from forest soils. That calcium depletion has had devastating effects on trees, especially sugar maples and red spruce. Acid rain leaches calcium from the needles of red spruce, making them more susceptible to cold. It also leaches calcium and magnesium from the soil, which can stress sugar maples. In addition, acid rain allows aluminum to accumulate in the soil. When trees take up aluminum, their roots can become brittle.

Some researchers have tried adding calcium back into the forests to speed recovery. April is currently involved in one such experiment in the Adirondacks. Over the past four and a half years, the calcium has penetrated only the top 15 centimeters of forest soil. “It takes a really long time for [the calcium] to get back down into the soil,” April says, so it won’t be a quick fix.

April would like to see sulfur dioxide and other emissions curtailed even further. “We still have acid rain coming in,” he says. “Some lakes look like they might be ready to come back, and if we cut the emissions more they would.”

Princeton University’s Michael Oppenheimer, who was a key player in the acid wars as chief scientist for the conservation group Environmental Defense Fund, agrees. “I think sulfur dioxide and nitrogen oxide need to be effectively eliminated,” he says. “We ought to head towards zero and see how close we can get.”

Although some effects of acid rain are lingering, most scientists consider it an environmental success story. “Science identified the problem. Science provided the guidelines for how to try to resolve the problem,” Likens says. “The success is that we have taken action as a society to try to deal with the problem.”

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The Legacy of EPA’s Acid Rain Research

Published August 18, 2020

In EPA’s 50 years of research, one of the most significant environmental challenges the nation faced was the problem of acid rain. Although evidence of acid rain’s harmful effects emerged centuries ago, it wasn’t until the early 1980s that it was recognized as a major threat. In taking part in the national effort to combat acid rain, EPA scientists helped usher in a new chapter of environmental science.

Acid rain forms mainly through reactions with the chemicals sulfur dioxide and nitrogen oxide found in fossil fuel emissions. It can take the form of acidic rain, snow, or dust and can travel hundreds of miles in the air before falling to the Earth’s surface. While normal rainwater is slightly acidic at a pH of 5.6, by 1980 the average rainfall in the United States was at a pH level of 4.6, about ten times more acidic and trending more acidic.

The effects of increasing acidity were widespread. Acid rain negatively affects aquatic and terrestrial life, damages structures by corroding metal, paint and stone, and threatens public health. In the early to mid ‘80s, scientists observed that many lakes and streams were becoming too acidic to support fish, amphibians, and other aquatic life. On land, acid rain was stripping nutrients from soil and foliage that plants needed to grow. Acid rain also contributed to increased weathering of buildings, statues, and gravestones.

In 1980, Congress directed EPA, along with five other federal agencies, four national laboratories, and partners from the private sector to form the National Acid Precipitation Assessment Program (NAPAP). With increased funding to investigate acid rain, NAPAP scientists achieved a greater understanding of acid rain in just a few years.

EPA scientists played a major role in several of the program's research areas, providing support for policies like the Acid Rain Program, which helped achieve major reductions in sulfur dioxide and nitrogen oxide emissions. These research efforts contributed advancements that reverberate through the scientific community to the present day.

EPA ecologist Paul Ringold, Ph.D., joined NAPAP in 1984 and continued to focus on acid rain for a decade. "EPA had a couple of visionaries who were involved in acid rain research," he said, "and in order to address the policy questions of acid rain, they did things that revolutionized the practice of environmental science."

Monitoring the nation's waters

One of the biggest impacts of acid rain was its effects on surface water, especially in lakes in Northeastern U.S. and Canada, which exhibited higher sensitivity to acidifying chemicals. To answer questions about acid rain’s impact on these lakes, scientists needed to develop new approaches to studying ecology.

Dr. Ringold explained that in the past, many ecologists tended to study individual sites in-depth—so, while scientists understood the impact of acid rain on specific lakes, they needed to look at the population of lakes to understand the extent of the problem and to respond to key science questions.

"The key questions on the ecological side were, how many acid lakes are there, and how many of them have become acidic as a result of acid rain?" Dr. Ringold said. "And, if we change acid rain, how will we change the number of acidic lakes?"

In 1983, EPA began the National Surface Water Survey to investigate the effects of acid rain on America's lakes and streams. Instead of attempting the impossible feat of sampling every lake and stream, researchers used statistical sampling methods to narrow down which were most likely to be susceptible to acid rain.

This approach to ecological research revolutionized the way EPA and similar federal programs developed datasets to monitor the environment, according to Dr. Ringold. The methods developed to answer questions about acid rain translated to other environmental questions, laying the groundwork for later monitoring programs like EPA's Environmental Monitoring and Assessment Program (EMAP) and the National Aquatic Resource Surveys (NARS). Both EMAP and NARS have advanced environmental monitoring practices and provided critical data on the health of the nation’s ecosystems.

Innovations in atmospheric modeling

Robin Dennis, Ph.D., spent 30 years in EPA's former National Exposure Research Laboratory before retiring in 2015. Soon after he joined EPA in the mid-'80s, Dr. Dennis became involved in evaluating NAPAP's newly developed air quality model. The Regional Acid Deposition Model (RADM) enabled scientists to simulate how emissions interacted with the atmosphere to form acid rain, and where it would be transported and deposited. Dr. Dennis explained RADM was instrumental in answering questions about acid rain because it modeled atmospheric chemistry more accurately than other models used at the time.

"The nice thing about what EPA had done is we pulled together the tools needed to see the whole causal chain of acid rain deposition," Dr. Dennis said. "Hardly anybody has the luxury of that kind of a complete causal chain being modeled and studied."

The methods behind RADM carried over into the present-day Community Multi-scale Air Quality (CMAQ) modeling system, now a key model for air quality management. Donna Schwede is a physical scientist in ORD's Atmospheric and Environmental Systems Modeling Division. She said her team's work developing CMAQ is important for "predicting acid rain or wet deposition values, as well as looking at the ability of different proposed control strategies to reduce acid rain and its harmful effects on ecosystems." 

Today, EPA continues to work to understand the impacts of acid rain through measurement and modeling. Scientists from EPA are active participants and leaders in the National Atmospheric Deposition Program, which monitors the chemistry of precipitation in the U.S. as part of the National Trends Network.

"We also continue to improve our modeling capabilities for atmospheric deposition," Schwede said. "While SO2 emissions have been greatly reduced, other pollutants can also be acidifying, and controlling those emissions remains a challenge."

While some pieces of the acid rain puzzle remain, EPA scientists have played a critical role in the effort to mitigate the effects of acid rain, then and now. To date, initiatives like the Acid Rain Program have had great success in reducing the emissions causing acid rain. The national average of  SO 2  annual ambient concentrations decreased 93 percent  between 1980 and 2018. Wet sulfate deposition – a common indicator of acid rain –  decreased 86 percent  reduction from 2000-2002 to 2016-2018. Data from EPA’s Long-Term Monitoring program show marked improvements in the acidification of lakes and streams, while better air quality has led to a decrease in adult mortality and will prevent an estimated 230,000 premature deaths this year alone. In their work to address acid rain, EPA scientists not only advanced the field of environmental science, but also helped achieve substantial benefits for the environment and human health.

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Case studies

The Tindall Limestone and Oolloo Dolostone aquifers are important groundwater stores. The dry-season flow (May–October) for parts of the Daly River system is mostly dominated by input of groundwater from these 2 underlying aquifers. The aquifers are also a primary source of water for human consumption, with more than 80% of local water use being sourced from groundwater.

A key groundwater level of the Tindall Limestone Aquifer is located near Katherine; a key bore for the Oolloo Dolostone Aquifer is located near the junction of the Douglas and Daly rivers.

In 2020, for the second consecutive year, the normal increase in groundwater levels during the wet season in the Tindall Limestone and Oolloo Dolostone aquifers did not occur because of poor wet-season rainfall (Figures 8 and 9). Except for a few minor increases in groundwater levels following rainfall events, levels in both aquifers declined for most of the year. At 30 June 2020, groundwater levels in the Tindall Limestone Aquifer were the lowest in more than 20 years; levels in the Oolloo Dolostone Aquifer were the lowest on record (since 2006) ( BOM 2020f ) .

m = metre

Source: BOM (2020f)

Data are lacking on the volumes of water stored in the aquifers; however, information on the total annual change in aquifer storage is available. In the Daly River aquifers, there have been 7 annual drops in storage during the past 9 financial years, reflecting a sustained period of relatively poor wet-season rainfall in the region (Figure 10). The very large increase in storage in 2011–12 was primarily attributed to well-above-average rainfall over a 2-year period associated with the 2010–12 La Niña event ( BOM 2020g ) .

ML = megalitre

Source: BOM (2020g)

Ciaron Dunn, Cooks River Alliance

The Cooks River begins as a series of small watercourses near Graf Park in Bankstown and flows for 23 km east towards Botany Bay/Gamay, flowing through some intensely urban and former industrial landscapes. The care and control of the river are complicated: responsibility is shared between 7 local councils (Strathfield, Burwood, Inner-West, Bayside, Georges River, Canterbury Bankstown, Sydney City), the Metropolitan Local Aboriginal Land Council, Sydney Water, the New South Wales Government and industry.

Integrated catchment management (ICM) approaches sustainable resource management from a whole-of-catchment perspective, recognising the interrelationships between freshwater, marine and terrestrial flora and fauna ecosystems. If addressed in an integrated way, catchment management can ensure conservation and sustainable use of biodiversity in conjunction with other objectives. For example, tree planting for groundwater or riparian (streamside) management can contribute to biodiversity conservation.

Management at a catchment level will help reduce the adverse impacts of built living environments and is an important aspect of overall coastal zone management. Nutrients, sediments and other pollutants arising from within catchments have a significant impact on the health of coastal and marine ecosystems.

Another benefit of the ICM approach is the involvement of all elements of the community. ICM is a very effective way of engaging all the community, including those involved in land-use planning, natural resource management, primary production and conservation, in working together to improve the overall management of their local area.

Cooks River Alliance

The Cooks River Alliance has been established to restore, rehabilitate and renew river vitality. To achieve longer-term success, 8 goals across 3 strategic focus areas have been developed. The focuses are:

• valued partnerships
• catchment health advocacy
• community action.

One of the most important partnerships is with Aboriginal people and organisations in the catchment. Two projects have resulted from consistent consultation and active engagement between the alliance and key representatives from local Aboriginal communities: an Aboriginal history along the Cooks River catchment and the Aboriginal Traditional Ecological Knowledge project.

Other outcomes include the renaming of a wetlands site, hosting of a Culture and Country Day, employment of 35 contractors with Aboriginal heritage, recording and exhibition of 12 oral histories from local people and publication of a book. On-ground works have included construction of 7 rain gardens, with water quality monitoring from 2 of them, and completion of a restoration to wetlands at Landing Lights Wetland.

With communities, 3 major events have been coordinated, more than 300 school students have been introduced to water-sensitive urban design, almost 1,500 community members have been introduced to stormwater management challenges, and more than 10,000 bags of rubbish and weeds have been collected. The alliance has also coordinated publication of 3 ecological health report cards for the Cooks River, launched a new website and produced 9 short films in 7 languages to inform communities about the connections between community action on water and stormwater pollution.

An alliance of connected community and Cooks River catchment land managers is continuing to maintain and improve river catchment health.

Health of the river

The ecological health of the Cooks River has been monitored and evaluated for the following indicators: freshwater benthic macroinvertebrates, water quality, riparian vegetation and benthic diatoms. Sampling is based on subcatchments, rather than sites, and the indicators used are common measures used for waterway assessment. Monitoring results allow strategic and targeted on-ground activities to improve the conditions in the catchment.

Across 5 sites within the catchment, moderate to extreme degradation is indicated, especially in riparian zones that display high degrees of weed invasion. Water quality across freshwater areas is described as fair. All sites have elevated nutrients and turbidity, reflected in diatom populations.

Cooks River Catchment Coastal Management Program

Integrated catchment and coastal management is a complex and challenging task, especially in highly developed and urbanised areas like the Cooks River catchment. The Cooks River Catchment Coastal Management Program (CMP) Stage 1 Scoping Study has developed a shared understanding of the Cooks River catchment and coastal management issues and priorities. The study builds on work by councils, the Cooks River Alliance, state agencies and other stakeholders over several decades.

The scoping study is expected to identify an overall purpose, a clear vision statement and accountable objectives for the CMP. A triple-bottom-line approach was used to identify environmental, social and economic values by their relevance to the Cooks River catchment study area, and their local and broader community benefits. The key coastal and management issues to be addressed by the CMP were identified by establishing the main threats to these values.

The Narran Lakes/Dharriwaa have long played an important role for Indigenous people. The Narran Lakes have significant Indigenous cultural value, and are the site of many important Indigenous artefacts, including a rock quarry. In the past, these rocks were used to make tools and to trade between tribes, and there is extensive archaeological evidence of a long history of Indigenous use and occupation of the lake system. The lakes were a rich source of food and other resources for Indigenous people, and were an important meeting and trading place for Euhlaroi, Euahlayi, Kamilaroi, Murawarri, Ngemba, Ngiyampaa and Wayilwan people. Further afield, the Barkandji, Bigambul, Kooma and Mandandanji people also have cultural connections with the Kamilaroi and Euhlaroi/Euaylayi ( Davies et al. 2020 ) .

The Narran Lakes wetland system is an internationally recognised Ramsar wetland and an important waterbird habitat. Endangered native waterbirds rely on the lakes to breed and survive.

Between 2017 and 2019, long-term rainfall deficiencies developed in the Condamine–Balonne catchment, particularly the Upper Condamine (Figure 22). The 2019 rainfall was the lowest annual rainfall on record for the catchment since 1911. At only 177 mm, it was 50 mm lower than the nearest record set in 1915, and 121 mm lower than the 298 mm received in 2006 at the peak of the millennium drought.

The lack of rain affected soil moisture, water storages, groundwater and river flow, and the human and environmental systems that rely on them. The total volume of water in the major storages in the region fell to 4% in January 2020, the lowest since 2009, with Beardmore water storage at only 2% (Figure 23).

In February 2020, most of the Condamine–Balonne catchment received 25–200 mm of rain. The rain was widespread and delivered through a series of rain bands. The February rain started the rivers flowing and weirs filling. Beardmore water storage went from 2% to 100% in only 8 days and started spilling on 15 February.

Source: BOM (2020h)

The water started to make its way down the system from early February. Flow in the Balonne River peaked north of St George at Weribone at more than 160 gigalitres/day before joining the flow from the Maranoa River and quickly filling Beardmore and Jack Taylor water storages. The water then spilled out across the landscape through the braided rivers system and floodplains of the lower catchment.

One of the great beneficiaries of this flood event was the Narran Lakes wetland system, which receives water during large flows in the lower Balonne River. Flow into the wetlands was aided by Queensland water-planning rules, water from Commonwealth environmental licences and voluntary contributions to environmental flows from irrigators in the catchment. Major flows first reached the wetlands on 29 February and peaked on 20 March – the first significant inflows in 8 years (Figure 24).

Photos: Commonwealth Environmental Water Office

Zena Cumpston, 2021

The Brewarrina fish traps (Figure 26) are located within the Barwon River in north-west New South Wales. Although they are located in Ngemba Country, they are highly culturally significant not only to the Ngemba people but to many other Aboriginal nations that are known to have traversal rights related to the shared use of the fish traps. The site is known not only for the use of fish traps but as a significant meeting place for cultural business and law used by many Aboriginal nations, including the Morowori, Weilwan, Barabinja, Nuaalko, Kula, Ualarai and Kamilaroi nations ( Rando 2007, MPRA 2015 ) .

The fish traps are traditionally known as Baiame’s Ngunnhu. Baiame is the ancient creator being of many south-eastern Australian Aboriginal nations. The Murdi Paaki Regional Assembly is the peak Aboriginal governance body for the Murdi Paaki Region, representing the interests of Indigenous people throughout western New South Wales. Its website explains ( MPRA 2015 ) :

According to Aboriginal tradition, the ancestral creation being, Baiame, created the design by throwing his net over the river and, with his 2 sons Booma-ooma-nowi and Ghinda-inda-mui, built the fish traps to its shape. But according to oral history, the fish traps (and the technology behind them) were inspired by nature – by the pelican, with the traps acting like a pelican’s beak to scoop fish out of the water.

The fish traps are a structure that once encompassed several hundred stone traps, with many family groups across multiple neighbouring nations responsible for their use and maintenance. The traps and the many significant cultural sites that surround them provide a link between pre- and post-contact people and events, as well as showcasing traditional knowledge, Indigenous innovation, lifestyles, intertribal relationships and cultural practice ( Rando 2007 ) . In the past, Brewarrina was a place where groups met both formally and informally, largely mediated by the use of the fish traps. Organised gatherings were cultural festivals that included important initiation and other cultural business, as well as intertribal contests and games. It is known that these gatherings attracted huge groups of many thousands of people ( Dargin 1976 ) . However, stones were removed by settlers and colonisers to accommodate paddle steamers and were also taken to be used in roads and buildings ( Maclean et al. 2012 ) .

Photo: B Moggridge

Baiame’s Ngunnhu continues to be used as a cultural and meeting place by many groups today. The fish traps, although damaged by the many continuing intrusions of colonisation, are still in use ( Dargin 1976, Commonwealth of Australia 2005 ) .

In 2005, when the fish traps were included on the National Heritage List, it was noted ( Commonwealth of Australia 2005 ) :

Aboriginal people used the unusual combination of a large rock bar, seasonal river flows and suitable local rocks to develop the Ngunnhu. It is nearly half a kilometre long and consists of a series of dry-stone weirs and ponds arranged in the form of a net across the Barwon River. The size, design and complexity of the Ngunnhu is exceptionally rare in Australia … The structure of the Ngunnhu demonstrates the development of a very efficient method for catching fish involving a thorough understanding of dry-stone wall construction techniques, river hydrology and fish ecology … The role of an ancestral being (Baiame) in creating built structures is extremely unusual in Aboriginal society and makes both the structure (Ngunnhu) and the story nationally important.

Baiame’s Ngunnhu is a complex, engineered system that is considered to be one of the oldest human-made structures on Earth, and yet somehow remains little known and under-resourced ( Tan 2015 ) .

A 2012 report by CSIRO undertaken as part of a project with Traditional Custodians identified a keen interest from Traditional Owners in collaborative research aimed at illuminating the potential for Indigenous hydrological knowledge to contribute to current water management challenges, and a desire for promotion and conservation of their water-related knowledge ( Maclean et al. 2012 ) . This extensive report included work with Ngemba community members to identify the challenges they experience in fulfilling their water management interests and cultural obligations. These challenges include:

• highly dominant western water paradigms that fail to recognise Aboriginal values and the water needs of the river as a spiritual entity separate from human requirements
• a lack of leadership capacity building to bolster community efforts to care for Country, and to meaningfully partner and engage with water planners
• difficulties in resourcing and coordinating beneficial water-related projects and programs within the community
• the need for implementation of Aboriginal water values to ensure that water allocations bolster the spiritual and environmental health of the old mission billabong, the fish traps and the Barwon River
• the need to develop local sustainable livelihood opportunities, such as those that would arise from expanded and better-resourced tourism opportunities.

Baiame’s Ngunnhu is a cultural landscape that facilitates a direct link to ancestors and illuminates cultural knowledge, heritage, practice, histories, belonging and wellbeing. The centrality of water to Aboriginal people and all aspects of their lives and heritage is illuminated in this quote from a Ngemba community member ( Maclean et al. 2012 ) :

(The) river is the essence, without it we are all dead, spiritually. It plays a crucial part in Aboriginal culture. River holds very special liquid – water, water is not separate from the river, which is what they are doing now (irrigation), the river holds the essence of life, water gives life, not just to you and me, to the trees, the birds, fish, spirit. Water keeps the spirit alive. If the spirit is not working properly, you will be sick … spirit is the foundation of Aboriginal culture. It is an unseen element, a crucial element. (Ngemba, interviewee 1, series 1)

Source: Lucas (2019)

In 2019, Budj Bim Cultural Landscape was entered on the United Nations World Heritage List – the 20th Australian site to make the 1,100-strong list – alongside Uluru, the Daintree Rainforest, the Great Barrier Reef and Melbourne’s Royal Exhibition Building ( Lucas 2019 ) .

Budj Bim, on a site about 40 km north of Portland (Figure 28), is the first Australian World Heritage site to be listed exclusively for its Indigenous cultural values. Engineering works built over generations at Budj Bim allowed the Gunditjmara people to trap eels in a complex system of weirs, constructed channels, and holding and growing ponds. These supplied them with enough food to sustain them year-round in villages of stone huts, and to undertake trade. The aquaculture system was created 6,600 years ago and has since been in use by the Gunditjmara people.

Adding Budj Bim to the United Nations World Heritage List challenges the common belief that Australia’s First People hunter–gatherers without permanent settlements. Instead, the site shows evidence of a complex Aboriginal economy and settled lifestyle, in which the country was managed and modified. Most Gunditjmara thought of the landscape in this part of western Victoria as being changed by pastoralists who came from Europe and removed rocks to create vast tracts of grazing land. The Gunditjmara people demonstrated at Budj Bim that manipulation of the landscape was possible in an entirely more sympathetic way (Figure 29).

Photo: Ian McNiven, courtesy Gunditj Mirring Traditional Owners Aboriginal Corporation

In May 2019, the Victorian Government committed $5.7 million for preserving and promoting Aboriginal heritage, in large part to complete the master plan for Budj Bim, in anticipation of an increase in global attention resulting from the World Heritage listing.

Gunaikurnai Land and Waters Aboriginal Corporation (GLaWAC) represents Traditional Owners from the Brataualung, Brayakaulung, Brabralung, Krauatungalung and Tatungalung family clans, who were recognised in the Native Title Consent Determination, made under the new Traditional Owner Settlement Act 2010 , the first such agreement under that Act.

On behalf of its members, GLaWAC will receive 2 gigalitres of unallocated water in the Mitchell River. This is a first and momentous outcome for the Gunaikurnai people, and it recognises the importance of gaining rights to water to restore customary practices, protect cultural values and uses, gain economic independence and heal Country. It is an important outcome of the Water for Victoria policy, released by the Victorian Government in 2016. Securing water rights for the Gunaikurnai people puts the ‘Waters’ into the Land and Waters Aboriginal Corporation for the first time, and GLaWAC thank all our partners in government and the local community for their support.

Reference: Mooney & Cullen (2019)

National Cultural Flows Research Project 2018

Source: MDBA Water Quality Advisory Panel, February 2021

Lake Hume is located near Albury (New South Wales)–Wodonga (Victoria) and is the main operating storage of the River Murray system, supplying water for irrigators, cities and towns, and environmental purposes.

During the 2019–20 bushfires, approximately 32% of the Lake Hume catchment was severely burned, making it highly susceptible to increased mobilisation of sediment, ash, nutrients and other contaminants following rainfall events.

In February 2021, significant rainfall was recorded across the bushfire-affected areas of the upper Murray, resulting in run-off containing large amounts of ash, sediment and debris. It also contained large amounts of dissolved organic carbon, iron, manganese and nutrients.

With seasonally warmer temperatures, this material triggered biological and chemical processes within Lake Hume that saw development of a significant layer of water with very low dissolved oxygen.

Across the warmer months, Lake Hume typically becomes layered with thermally stratified water. During the event, the water with little or no dissolved oxygen occurred in a layer at a depth of approximately 20 m, which is around the same level as the Hume Dam offtakes.

This resulted in water being released with low dissolved oxygen levels into the River Murray immediately downstream from Hume Dam with the following impacts:

• Murray crayfish reported to be crawling out of the water in response to low dissolved oxygen
• ‘rotten egg’ odour (hydrogen sulfide) and orange staining of vegetation and some of the crayfish due to oxidation of iron and manganese
• water quality supply issues reported by Albury City Council, with ‘rotten egg’ odour and discolouration.

The Murray–Darling Basin Authority responded by adjusting operations to assist with aeration of the water, and applying compressed air to water flowing through the Hume Dam hydropower station.

Ongoing response includes upgrades to upstream and downstream water quality monitoring sites, adaptive management of releases (if required) and engagement of water quality expertise to quantify potential risks.

Source: Yorta Yorta Nation and Elders

The Murray River determines the New South Wales and Victorian borders. The Barmah Choke restricts the flow capacity of the Murray River to around 9,600 megalitres (ML) per day; this has decreased to 7,000 ML per day or less due to the accretion of sands on the Barmah Choke (Pama Narrows) riverbed. River managers need to consider the impacts of using the Choke to deliver water downstream for agricultural and consumptive purposes ( MDBA 2021e ) .

The Elders of Yorta Yorta Nation have begun a Yorta Yorta investigation into water impacts on the Pama Narrows to determine the impact of flow regulation on Yorta Yorta knowledge, stories, people and sites, including middens, mounds and scarred trees. Yorta Yorta have engaged a drone specialist to assist with telling their story visually. The investigation aims to preserve their traditional story, culture and identity intact.

Zena Cumpston

In 2021, 123,000 tonnes (t) of almonds are projected to be harvested in Australia. Almonds now represent Australia’s most valuable horticultural crop, and Australia is the world’s second largest supplier ( ANIC 2019, Granwal 2020, Jeffery et al. 2021 ) . For each tonne of almonds sold in Australia, 2.6 t are exported; in 2019–20, these were sold to more than 50 countries, with the almond industry yielding $772.6 million ( Almond Board of Australia 2021 ) .

In 2000, Australia had approximately 3,546 hectares (ha) of almond tree plantations. By 2019, the rapid expansion of this industry had increased almond-growing land to 53,014 ha – a 900% rise in less than 20 years ( Schremmer 2020 ) . The fact that much of this expansion has occurred in a short time, particularly within the highly compromised Murray–Darling Basin, invites questions about the water needs of almonds and the role of this crop in the multiple pressures on inland water and the environment in Australia more widely ( Bleby 2019 ) .

In Australia, almonds use triple the amount of water required to produce wheat or feed grain; they need at least 8.5–10 megalitres of water per hectare during a growing season that stretches from October to April ( Fulton et al. 2019 ) . The underlying need for a reliable supply of water sees almond crops planted along river systems that are facing increasing pressure from prolonged dry periods. Almond crops have grown by 50% in the Murray–Darling Basin since 2016, despite their substantial water requirements in a geographical area with severe and catastrophic water security issues ( Mann 2021 ) . Almonds deplete biodiversity because they are grown as monocultures, with industrial farms stripping the ground around the trees bare to treat for insects and fungi. Also concerning is that the pesticides used to ensure high yields are particularly lethal to bees ( McGivney 2020 ) , and almond cultivation requires more hives for pollination than any other crop ( Mann 2021 ) .

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• Published: 12 February 2024

Impact of simulated acid rain on chemical properties of Nyalau series soil and its leachate

• Mohamad Hilmi Ibrahim 1 ,
• Susilawati Kasim 2 ,
• Osumanu Haruna Ahmed 3 ,
• Mohd. Rashid Mohd. Rakib 4 ,
• Nur Aainaa Hasbullah 4 &
• Md. Tariqul Islam Shajib 5   nAff6  

Scientific Reports volume  14 , Article number:  3534 ( 2024 ) Cite this article

1183 Accesses

Metrics details

• Environmental sciences

Greenhouse gases can cause acid rain, which in turn degrades soil chemical properties. This research was conducted to determine the effects of simulated acid rain (SAR) on the chemical properties of Nyalau series ( Typic paleudults ). A 45-day laboratory leaching and incubation study (control conditions) was conducted following standard procedures include preparing simulated acid rain with specific pH levels, followed by experimental design/plan and systematically analyzing both soil and leachate for chemical changes over the 45-day period. Six treatments five of which were SAR (pH 3.5, 4.0, 4.5, 5.0, and 5.5) and one control referred to as natural rainwater (pH 6.0) were evaluated. From the study, the SAR had significant effects on the chemical properties of the soil and its leachate. The pH of 3.5 of SAR treatments decreased soil pH, K + , and fertility index. In contrast, the contents of Mg 2+ , Na + , SO 4 2− , NO 3 − , and acidity were higher at the lower SAR pH. Furthermore, K + and Mg 2+ in the leachate significantly increased with increasing acidity of the SAR. The changes in Ca 2+ and NH 4 + between the soil and its leachate were positively correlated (r = 0.84 and 0.86), whereas the changes in NO 3 − negatively correlated (r = − 0.82). The novelty of these results lies in the discovery of significant alterations in soil chemistry due to simulated acid rain (SAR), particularly impacting soil fertility and nutrient availability, with notable positive and negative correlations among specific ions where prolonged exposure to acid rain could negatively affect the moderately tolerant to acidic and nutrient-poor soils. Acid rain can negatively affect soil fertility and the general soils ecosystem functions. Long-term field studies are required to consolidate the findings of this present study in order to reveal the sustained impact of SAR on tropical forest ecosystems, particularly concerning soil health, plant tolerance, and potential shifts in biodiversity and ecological balance.

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Introduction.

Acid deposition poses several threats to ecosystems by affecting plant health, diversity and structure, including processes and functions in the ecosystem 1 , 2 . Acid deposition is defined as accumulation of undesired chemical compounds in the atmosphere at toxic concentrations 3 . Acid deposits are materials (solids, liquids and gases) occurring in excess quantities from the average amount and present at the lowest layer of the atmosphere 4 . Acid deposition in the atmosphere can be attributed to diverse chemical compounds originating from fossil fuel combustion, agriculture, mining, and manufacturing activities. Acid deposition is a global threat that has been shown to result in various environmental and human health hazards such as depleting essential nutrients and increasing toxic metals, which can lead to reduced plant growth and biodiversity 5 , 6 , 7 .

Acid deposits refer to rain, snow, fog, particulates, and gases, whereas acid rain only refers to rainwater at pH below 5.6 8 , 9 . Acid rain mainly consists of sulfur dioxide (SO 2 ) and nitrogen oxides (NOx) forming acidic compounds, whereas other greenhouse gases like Cl − and CO 2 , linked to climate change and global warming. These gases undergo complex chemical reactions in the atmosphere after which they fall to the earth’s surface as wet or dry deposition 10 . According to Zhang et al. 11 , acid rain with a pH of 5.6 is deemed normal as atmospheric CO 2 at a pressure of 101 kPa and temperature of 20 °C lowers rainwater pH from 7 to 5.6. This normalcy shifts when gases like N 2 O and SO 2 contribute to a further decrease in pH below 5.6 due to increasing hydrogen ion concentrations.

Soil fertility and soil physico-chemical properties such as soil nutrients for plant growth and production, are commonly affected by prolonged exposure to acid deposition 12 , 13 . Several scientific reports have demonstrated that acid deposition may disrupt nutrient cycling in soil habitats, particularly by deteriorating soil physico-chemical properties, especially its fertility 14 , 15 , 16 , 17 . For example, soil nutrient leaching in White Mountain National Forest in the Central New Hampshire, US, resulted from acid deposition 18 . In addition, other studies on the impact of acid deposition on ecosystems have revealed that this phenomenon affects species richness and diversity 19 , 20 and hydrological cycle, including water quality 21 .

More than that, this acidic precipitation lowers the soil pH, a process termed soil acidification. Research by Yang et al. 22 shows that acidification leads to nutrient leaching, particularly of calcium and magnesium, while increasing the solubility and toxicity of metals like aluminum and lead. This results in reduced soil fertility and damage to plant root systems, adversely affecting plant growth and crop yields, as noted by Dai et al. 23 . Furthermore, soil acidification disrupts microbial communities, impacting critical processes like decomposition and nutrient cycling 24 .

Soil leaching is defined as the movement of nutrients from the upper soil profile to its lower depths 25 . Leaching typically causes soil pH to decrease with decreasing base cations concentrations. When acid deposition occurs, there is an increase in the solubility of heavy metals and Al mobilization in soils 26 . To this effect, accumulation of H + ions reduces soil pH while increasing the solubility of heavy metals and Al mobilization. The leaching of macronutrients occurs due to the replacement of H + ions by acid rain, which increases soil acidity to levels that compromise fertility 27 . This phenomenon of soil acidification is not just theoretical; it has been observed on a large scale, for instance, in Southern China, where soil acidification was documented after 20 years of continuous exposure to acid rain 28 , 29 .

The mineral acid soils in Sarawak, Malaysia belong to four major series, namely Bekenu, Nyalau, Merit, and Stom series 30 . Nyalau series are the soils contaminated with eroded material from upslope areas with high content of sesquoxides 31 . According to Tan et al. 32 , Nyalau series belongs to Typic paleudults , therefore it is classified as acidic soils, with pH between 4.3 and 4.8 and CEC values below 24 cmol kg −1 . The textural class of these soils is sandy clay loam with brownish yellow to yellow colouration. In Malaysia, the cumulative acid loading from the atmosphere to terrestrial ecosystems has been on the increase since 2010–2019 33 . As a result, SO 2 and N 2 O composition in some states in Malaysia are 0.66 and 0.17 ppm, respectively 34 , while the pH of rainwater in selected industrial areas in Malaysia have reached 4.32 35 . EANET 36 reported the annual rainwater pH at Petaling Jaya, Tanah Rata, Danum Valley, and Kuching, Malaysia as 4.15, 5.01, 5.21, and 5.43, respectively.

According to Department of Environment of Malaysia (unpublished data), the total SO 2 emission in Malaysia was 0.25 ppm in 2020. Although this value is less than those of other countries, precautions should be taken to manage this occurrence to prevent it from increasing in severity. Although there are studies on simulated acid rain on soils in other areas 26 , 27 , 37 , 38 , there is dearth of information on the effect of SAR in Nyalau soils and its leachate. This study is important because the Nyalau series is not widely known. The Nyalau series, a tropical soil, is unique for its high sand content, strong acidity, and poor nutrient retention, making it challenging for agriculture but crucial for soil studies. Its characteristics and study are valuable for soil science and geology and contribute to our understanding of soil composition and geological history in certain regions facing the problem of acid rain.

This study embodies three objectives that significantly centre on the effects of simulated acid rain on chemistry and properties of Nyalau series ( Typic paleudults ) soil and its leachate. Firstly, the objective of the study is to identify the possibility of significant differences in soil fertility index and soil evaluation factor of Nyalau series soils when exposed to SAR. Secondly, the objective of the study seeks to ascertain the possibility of significant differences in the chemical properties of Nyalau series soils and its leachate when exposed to SAR. Finally, the study strives to examine the correlation and cluster between soil and leachate chemical properties across SAR pH. Soil fertility index and soil evaluation factor were used as key indicators to determine the effects of SAR on the fertility of Nyalau series.

Materials and methods

Soil collection, preparation and analysis.

The topsoil (0–20 cm depth) of Nyalau series from the undisturbed/minimal human intervention or alteration agricultural field, Universiti Putra Malaysia, Bintulu Campus, Sarawak, (03° 12.721′ N, 113° 4.477′ E) was collected from 10 points apart then bulked together using a spade until approximately 50 kg of soil (Fig.  1 ). The soil was collected in transparent plastic bags and transported to the laboratory, where it was air-dried in room temperature for a few days to a week and sieved to pass a 2 mm mesh. The initial chemical properties of the soil samples were determined using standard procedures as adopted from Tan 39 , for pH, Allen et al. 40 for CEC, K + , Ca 2+ , Na + , Mg 2+ and P, Keeney and Nelson method 41 for NO 3 − and NH 4 + , Rowell 42 , for acidity, Al 3+ , and H + and Cheftetz et al. 43 for soil organic matter and total organic carbon (Table 1 ).

Location of the soil sampling sites in Universiti Putra Malaysia, Bintulu, Sarawak. Sampling were conducted ramdomly from several points in study sites.

Leaching experiment design and setup

The experiment was conducted using 18 polyethylene soil columns having 16 cm diameter and 28 cm depth and fitted with 26 holes (3 mm in diameter) at the bottom. The holes evenly distributed in a uniform circular pattern for optimal drainage. Analytical grade tissue paper was placed at the bottom of the column (to prevent soil loss) after which the column was filled with 270 g soil. Soil bulk density 44 at the the undisturbed agricultural field site was first quantified, and the value was used to estimate the quantity of soil (i.e. soil without water content) to be used/ correspond with soil compaction in each column. This resulted in each empty soil column being filled with 270 g of air-dried soil, to simulate the natural condition of the Nyalau soil at the study sites. A tray was placed underneath each soil column to collect leachate.

Treatment preparation and application

The soil in the columns were exposed to SAR by applying water with pH of 3.5, 4.0, 4.5, 5.0, 5.5, and 6.0.The pH 6.0 served as natural rainwater (control treatment). The selected SAR pH values of 3.5, 4.0, 5.0 and 5.5 were chosen to represent a range of acid deposition scenarios, from extreme to more moderate conditions enabling the study of soil responses under different environmental stress levels. A pH of 3.5 represents the worst-case scenario for acid rain worldwide and indicates the most severe environmental impacts. The other values, 4.0, 5.0 and 5.5, serve as projections ranging from extreme acidity to normal rainwater conditions. This range provides a comprehensive understanding of how different acidity levels can affect ecosystems, making the study relevant to real-world scenarios.

Water with varying pH levels was prepared by adding 0.1 molar H 2 SO 4 and HNO 3 in a 3:2 volume-to-volume ratio to distilled water, after which the pH was adjusted to the desired level 45 . The chemical properties of the SAR are presented in Table 2 . Each treatment had three replications; thus, the total experimental units were 18. The experimental units were arranged in a completely randomized design (CRD) with aset up of 6 m × 4 m room having a 76% relative humidity and a temperature of 21 °C. Approximately 318 mL of SAR were applied to each soil column and this volume was based on the field capacity of the soil using a drip system operating at a flow rate of 2.71 mL s −1 . The soil in the leaching columns were exposed to the SAR once every three days for 45 days (15 applications in total) at 8 pm. SAR application interval was based on average monthly/yearly rainfall events in Bintulu (MMD, Unpublished data), Sarawak, Malaysia. At the end of the experiment, the soil and its leachate were collected for chemical analysis.

Analysis of selected chemical properties of Nyalau series

After the incubation experiment, the soil samples in the columns were collected, air-dried, and sieved to pass through a 2 mm sieve for chemical analysis. The soil pH was measured in distilled water at a soil/water ratio of 1:2.5 39 . The CEC in mg/kg of the soil was determined using 1 M ammonium acetate buffered at pH 7. Exchangeable base cations were extracted using 100 mL of 1 M ammonium acetate buffered at pH 7, after which the filtrates were analyzed to determine the concentrations of exchangeable K, Ca, Na, and Mg using Flame Atomic Absorption Spectrometery (AAS) (iCE 300, Thermo Fisher Scientific®, NSW, Australia). The concentration of available P in the soil filtrate was determined using a UV–VIS spectrophotometer (UV-1800, Shimadzu, Kyoto, Japan) operated at 820 nm wavelength after extracting the soils using Bray’s solution (0.03 N of ammonium fluoride, NH 4 Fl in 0.025 N of HCI) 40 .

Soil available NO 3 − and NH 4 + were determined using Keeney and Nelson method 41 followed by steam distillation 40 . Soil acidity, Al 3+ , and H + were determined using the titration method 42 . The soil available sulfate was extracted using 0.5 M of NaHCO 3 , after which the extract was analyzed using ion chromatograph IC-MS (AI300, PerkinElmer Inc., USA). The loss-on-ignition (LOI) method was used to determine soil organic matter and total organic carbon 43 . A 5 g of oven-dried sample (dried at 6 °C for 24 h) was weighed into a porcelain dish, placed in a muffle furnace, and heated at 300 °C for 1 h to determine soil organic matter content.

The Soil Fertility Index (SFI; Eq.  1 ) and Soil Evaluation Factor (SEF; Eq.  2 ) of Nyalau series were calculated using the formulas of Moran et al. 46 and Lu et al. 47 , respectively.

Analysis of selected chemical properties of leachate

The leachate pH was measured using a pH meter (S220, Thermo Fisher Scientific®, USA) whereas electric conductivity (EC), salinity, and total dissolved solids were determined using EC meter (S70, Mettler Toledo Co., USA). Exchangeable cations were determined using AAS (AA5000, PerkinElmer Inc., USA) whereas nitrite (NO 2− ), phosphate (PO 4 3− ), nitrate (NO 3 − ), and ammonium (NH 4 + ) were measured using UV-spectrophotometer (DR 2010, Hach©, USA).

Statistical analysis

One-way analysis of variance (ANOVA) was used to detect between-treatment before after which treatment means were compare dusing Duncan’s New Multiple Range Test (post-hoc analysis) at p  ≤ 0.05. Pearson’s correlation analysis was conducted to determine the relationship between the chemical properties of the soil and its leachate. In addition, Pearson’s correlation analysis was performed to analyze the response of soil and leachate variables across the pH of SARtreatment. The statistical analysis was performed using SAS version 9.4 48 .

Hierarchical cluster analysis (CA) was performed to find out similar groups of soil properties depending of origin (one soil type) and concentration. The CA was performed on the various chemical properties simulated acid rain and leachate, using a distance cluster between 15 and 20 49 , 50 . A distance criterion between two variables express how closely correlate within the group. Two cluster analyses by means of hierarchical dendrograms were performed by using SPSS 28.0 (IBM SPSS Statistics, USA) applied to the SAR and soil leachate. All these analysis collectively allowed for interpreting how SAR treatments affected soil and leachate composition, guiding conclusions on acid rain's impact.

Effects of simulated acid rain treatments on soil properties

Soil pH, K + , SFI and SEF significantly decreased with increasing acidity of SAR. As example, significant decrease in soil pH and SFI (2.21% reduction) were recorded when the soil was exposed to SAR with pH 4.0 and pH 3.5. Potassium ions in the soil decreased from 0.037 to 0.019 mg kg −1 (48.64% reduction). Contrastingly, Mg 2+ , Na + , SO 4 2− , NO 3 − , and soil acidity significantly increased with increasing acidity of the SAR. Relative to control (natural rainwater) the soil which was exposed to SAR with a pH of 3.5 increased Mg 2+ , Na + , SO 4 2− , NO 3 − , and acidity by 193.33%, 101.30%, 46.2%, 18.65% and 22.02%, respectively. Furthermore, significant reduction was observed in the level of Al 3+ , H + , and Zn 2+ in soils exposed to SAR with pH 5.0. However, the K + , Ca 2+ and Zn 2+ cations decreased with increasing acidity of SAR (pH 4.0 and below). Similarly, available P in the soil significantly reduced from 1.62 mg kg −1 at SAR of pH 6.0 to 1.43 mg kg −1 at pH of 4.5, whereas SAR with pH 3.5 recorded an available P value of 1.57 mg kg −1 . Furthermore, the Soil CEC, Ca 2+ , Fe 2+ , and NH 4 + fluctuated across the SAR treatments whereas SEF generally remained unchanged (Table 3 ).

Effects of simulated acid rain (SAR) treatments on leachate properties

There was significant increase in K + and Mg 2+ concentrations in leachate as SAR levels were decreased from 4.0 to 3.5 (Table 4 ). K + ions increased from 5.62 mg L −1 (SAR at pH 6.0) to 6.65 mg L −1 (SAR at pH 3.5) whereas Mg 2+ ions increased from 0.72 mg L −1 (SAR at pH 6.0) to 0.83 mg L −1 (SAR at pH 3.5). The Na + in the leachate significantly increased from 1.92 to 4.63 mg L −1 with increasing SAR acidity. The continued acidification reduced Na + in the leachate to 2.68 mg L −1 (pH 3.5). The leachate of PO 4 2− concentration did not significantly differences regardless of SAR pH. Other variables fluctuated across the SAR pH (Table 4 ).

Relationship between soil and leachate properties

The relationship between the soil and its leachate properties was analyzed to determine acid deposition's effect on nutrients leaching or retention by the Nyalau series. The Pearson’s correlation analysis revealed that the changes in Ca 2+ and NH 4 + between the soil and its leachate positively correlated and the Pearson’s correlation coefficient (r) values were 0.84 and 0.86, respectively. However, the NO 3 − in the soil and its leachate was correlated negatively (r = − 0.82). The correlation for the other variables were not significant (Fig.  2 ).

Trends of selected soil and leachate properties of Nyalau series ( Typic paleudults ) soil after exposure to simulated acid rain. Correlation analysis was conducted, and the relationship was indicated by the Pearson’s correlation coefficient (r) and probability level significant at p  ≤ 0.05.

Cluster analysis for soil and leachate properties

The findings of CA are presented in two hierarchical dendrograms representing soil (Fig.  3 A) and leachate (Fig.  3 B). The dendrogram for soil comprise 3 clusters (Fig.  3 A). NH 4 + and NO 3 − comprise first cluster and SO 4 2− , SFI, CEC and SEF comprise the second cluster and are associated with a low distance criterion around 1. The rest of the chemical properties acidity, pHwater, pH KCl , H + , Na + , Ca 2+ , Mg 2+ , Al 3+ , Cu 2+ , K + , Zn 2+ and Fe 2+ form the third cluster and they are associated in a very low distance at around 1. In Fig.  3 B, the first cluster contains Cu 2+ ,NO 3 − ,PO 4 2− , NO 2 − , NH 4 + , Mg 2+ , Cl − , Salinity and S 2− and they are positioned at a very low distance around 1. In the second cluster, pH, K + , Ca 2+ and Fe 2+ form a group with a distance of CA below 3 whereas electrical conductivity (EC) is placed separately than cluster 1 and 2 with a high distance criteria at 25.

Hierarchical dendrogram for chemicals properties found in soil ( A ) and leachate ( B ) using Ward’s method.

Simulated acid rain and natural rainwater on soil properties of Nyalau series

Generally, the SAR treatments, including control, initially decreased soil pH (4.84). The pH ofsoilwith SAR pH below 4.5 (Table 3 ) was significantly low and this may cause reduction in the soil fertility index. Additionally, the soil exchangeable Al 3+ and H + were significantly increased because aluminium hydrolysis increases with increasing soil acidity. For example, a complete hydrolysis of one mole Al 3+ ions produces three moles H + ions to further decrease soil pH and this chemical reaction reduces soil CEC. This finding corroborates that of Zhang et al. 11 who explained that acid rain increases soil acidity and H + ions, leading to loss of mineral structure. Loss in mineral structure has been implicated in soil fertility decline. Wei et al. 51 also reported that acid rain reduces soil fertility because it reduces soil pH and cation retention capacity.

Although soils have strong pH buffering capacity, the SO 4 2− , H + , NO 3 − , and NH 4 + in acid rain favour the dominance of H + ions on the soil exchange sites such that soil CEC is disproportionately dominated by hydrogen ions instead of base cations, especially K. Significant leaching of K + in soil with SAR at pH 3.5 was expected due to the high acidity ofthis treatment. The dominance of stronger complementary adsorbed cations at the soil exchange sites could partly explain the loss of K into the leachate 26 , 51 . Acidic rainwater gradually diminishes exchangeable cations in topsoil because it facilitates changes in the nutrient pool and leaching of nutrients from the soil profile 44 . This observation is supported by Zhang et al. 11 , who reported significantly higher effluent K + concentration of SAR at pH 3 and below.

The low SAR pH were responsible for low variations in Ca 2+ , Mg 2+ , Na + , acidity, NH 4 + , and SO 4 2− in the soils compared with soil treated with natural rainwater. This finding is similar to that of Rampazzo and Blum 52 who reported that exposing parent rock material to acid rain, inspite of having 30–80% calcite, reduced CEC and base saturation, particularly Ca contents. This suggests the fertility and the overall productivity of soils will decline if they are exposed to acid deposition for a long time. A notable reduction in soil pH enhances the solubility of aluminium, consequently elevating the concentration of Al 3+ ions in the leachate. This finding aligns with Mulder et al. 53 observation, where they reported the phytotoxic effects due to increased dissolution of Al 3+ in soil leaching experiments conducted in both the Netherlands and New Hampshire, USA.

Soil Zn 2+ solubility has increase with decreasing pH (3.5–6.0) because the solubility of Zn decreases with increasing soil pH. High levels of soil contamination, with soluble Zn 2+ reaching 19,570 mg/kg and Cu 2+ up to 322.4 mg/kg 38 , enhance the phytoavailability of heavy metals 14 , leading to increased uptake by plants. The very acidic SAR treatments increased soil exchangeable sulfate 46.20% because of sulfate adsorption to form sulfuric acid which upon decomposing, releases H + and SO 4 2− ion. This reaction occurs at low soil pH 54 . Soil available ammonium increase with increasing acidity of SAR. The increase in NH 4 + concentration is consistent with the report of Johnson et al. 55 , who demonstrated that acid rain increases nitrogen mineralization and nitrification in forest soils.

Simulated acid rain and natural rainwater on leachate properties of Nyalau series

Leachate pH was highest with lower SAR pH compared with natural rainwater. According to De Walle et al. 56 , the increase in leachate pH was due to the accumulation of base cations, especially Ca 2+ and Mg 2+ (Table 4 ). This result also explains the movement of Ca 2+ and Mg 2+ down the soil profile, corroborating the results of Zhang et al. 11 on Latosol of Southern China. Low electrical conductivity and salinity values were recorded with lower SAR pH because the accumulation of base cations in the leachate increased the EC of the soil. The base cations in the leachate of the lower SAR pHs were higher than with the natural rainwater (Table 4 ). This present study suggests that acid rain causes leaching of the bases and this could cause ground water pollution through enrichment through lost nutrients from the soil profile.

Overall implication of varying simulated acid rain on soil and leachate properties

The incubation of Nyalau soil series with SAR generally had negative effects on pH, K, Fe and NO 3 of the soil and its leachate. This includes a decrease in soil pH, indicating increased acidity, and reductions in the concentrations of potassium (K), iron (Fe), and nitrate (NO 3 ) in the soil. The results indicate that when the pH of SAR decreases from 6.0 to 3.5, the pH and potassium (K) content in the soil and leachate also decrease. This is confirmed by the data in Tables 3 and 4 . The increased soil acidity with the low pH SAR is related to high H + concentration. The accumulation of H + from acid deposition increased the soil acidity 27 , 51 . Increase in the soil acidity through acid deposition might have affected the solubility of heavy metals such as Fe, as observed in the soil with low SAR pH. Furthermore, acidic pollutants can cause P fixation by Al and Fe in soils 57 and this explain low available P content in this present study (Table 3 ). The positive relationship between soil and leachate for Ca 2+ and NH 4 + was due to insufficient time (45 days) for leaching of cations from the soil. This slower leaching rate is due to the complex interplay of physical, chemical, and environmental factors within the soil. Essentially, these ions are not as readily mobilized or washed out of the soil compared to other elements, indicating a delayed response to the leaching process influenced by soil composition and conditions 58 .

More than that the similarities of SO 4 2− , SFI, CEC and SEF in hierarchical dendrograms of soil have shown that the fertility of Nyalau series soil have also influenced by SO 4 2− . We believe it was happening because of the presence of sulphuric acid (H 2 SO 4 ) from SAR treatments. Our argument is consistent with finding in Table 3 recorded higher SO 4 2− content under low SAR pH treatments. Similar study reported by Hüttl and Frielinghaus 59 in Eastern, Germany who shows that air pollutant or acid rain content with H 2 SO 4 could reduce the soil fertility accelerating soil acidification. In the leachate hierarchical dendrograms, there are similarities of soil water pH, K and Ca. This results reliable comes from accumulation of base cation while exposure to SAR as discussing in previous section.

Management implication of simulated acid rain on soil and leachate properties

Even with a short incubation study (45 days), we found a 2.21% reduction in the fertility of Nyalau series and 5.43% reduction in soil acidity as compared when exposed to natural rainwater (control treatment). The lower SFI of the soil in the present study (11.94) compared with research on a secondary forest in Lundu, Sarawak, by Perumal et al. 60 where SFI of 19.63 was recorded, indicates the prolonged negative impact of acid rain on soil fertility. These results showed that acid rain impacted soil and leachate properties, and it is possible that prolonged acid rain exposure will further modify soils of the Nyalau series detrimentally.

Therefore, for a comprehensive understanding of acid rain's effects, a long term study, possibly over a year, is recommended. This allows for observing long-term ecological and soil changes. Complementing this with advanced modeling would provide a holistic view, predicting future impacts and aiding in effective environmental management strategies, crucial for sustaining ecosystems and agricultural productivity in the face of environmental changes. Therefore, understanding the prolonged impacts of acid rain on soil properties is not only an ecological necessity but also crucial for human sustainability.

The study focused on the impact of simulated acid rain (SAR) on the Nyalau series soil, examining a range of acidity levels from less acidic (pH 5.5 and 5.0) to more acidic (pH 4.0 and 3.5). It was found that with increasing acidity, especially at pH 3.5, the soil experienced significant changes: a decrease in pH, potassium, and fertility, and an increase in magnesium, sodium, sulfate, nitrate, and overall acidity. The leachate from the soil also showed increased levels of potassium and magnesium, indicating a leaching effect that could lead to nutrient deficiencies for plants. The study also noted a positive correlation between changes in calcium and ammonium levels in both soil and leachate, and a negative correlation in nitrate levels, highlighting complex interactions between soil acidity and nutrient dynamics.

The results of our study have important practical implications for both land management and environmental policy. Land managers are suggested to regularly conduct comprehensive soil health assessments, especially in areas vulnerable to acid rain or soil acidification. These assessments should go beyond simply measuring pH and consider chemical properties such as K + , Mg 2+ and NO 3 − to inform soil treatment plans. In terms of policy, the observed deleterious effects of acidic treatments on soil properties call for stricter pollution regulations to curb acid rain, and the data could further guide the establishment of safe areas for agriculture and forestry based on the resilience of soils to acidification.

Data availability 

The datasets generated and/or analysed during the current study are available from the corresponding author upon reasonable request.

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Acknowledgements

The authors would like to acknowledge Department of Environment of Malaysia and Malaysia Meteorological Department for the providing atmospheric concentration data on 2020 and Bintulu temperature and rainfall data. We also aknowlwdge the technical support provided by Muhamad Fuad Ibrahim, Palanivell Perumal, UPMKB staff Arni Japar, Awang Marzuki Awang Mustapha, Elizabeth Andrew Anyah, and Awangku Ahmad Nizam Awang during the conduct of the research.

This research was funded by the Universiti Malaysia Sarawak under PILOT Research Grant Scheme (UNI/F07/PILOT/85193/2022), Ministry of Higher Education Education (Malaysia) under the Fundamental Research Grant Scheme (FRGS: 5523701), Universiti Putra Malaysia under the Research University Grant Scheme (RUGS: 9199765), Ministry of the Environment (Japan) under the Environmental Research and Technology Development Fund (B-0801), and Mitsubishi Corporation Trust Fund (6380500).

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Md. Tariqul Islam Shajib

Present address: Department of Natural Resources and Environmental Design, North Carolina Agricultural and Technical State University, Greensboro, NC, USA

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Agrotechnology Programme, Faculty of Resources Science and Technology, Universiti Malaysia Sarawak, 94300, Kota Samarahan, Sarawak, Malaysia

Mohamad Hilmi Ibrahim

Department of Land Management, Faculty of Agriculture, Universiti Putra Malaysia, 43400, Serdang, Selangor Darul Ehsan, Malaysia

Susilawati Kasim

Universiti Islam Sultan Sharif Ali, Kampus Sinaut, Km 33 Jln Tutong Kampong Sinaut, Tutong, TB1741, Negara Brunei Darussalam

Osumanu Haruna Ahmed

Faculty of Sustainable Agriculture, Universiti Malaysia Sabah, 90000, Sandakan, Sabah, Malaysia

Mohd. Rashid Mohd. Rakib & Nur Aainaa Hasbullah

Division of Soil, Water and Environment, Care to People Denmark, 2400, Copenhagen, NV, Denmark

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Contributions

[I.M.H] conceptualized the study, developed the main research framework, and was primarily responsible for the laboratory leaching and incubation study. He also contributed to data curation, methodology, and wrote the original draft of the manuscript. [K.S] played a pivotal role in data analysis and interpretation. She employed the necessary statistical tools to determine the correlations and were responsible for generating all the data charts and figures. [Author B] also assisted in writing and revising the manuscript, ensuring the technical details were articulated effectively. [A.O.H] managed the logistics and resources for the entire study. He supervised the application of SAR treatments to the soil samples and were instrumental in ensuring that standard procedures were adhered to. [Author C] also played a role in manuscript revision, particularly overseeing the accuracy and authenticity of the methodology. [M.R.M.R., H.N.A and I.M.T] contributed to the literature review and provided essential insights into the implications of the research findings, particularly concerning tropical forest ecosystems. They also assisted in drafting the discussion and conclusion sections of the manuscript and provided critical feedback for overall improvement.

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Ibrahim, M.H., Kasim, S., Ahmed, O.H. et al. Impact of simulated acid rain on chemical properties of Nyalau series soil and its leachate. Sci Rep 14 , 3534 (2024). https://doi.org/10.1038/s41598-024-52758-1

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Acid rain and acid gases in Australia

• Published: January 1989
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As a result of the demography of the country, geographic isolation and use of predominantly low-sulfur fuels, Australia does not have a high potential for acid deposition. Industrial emissions are small in scale compared with open sources, consequently the role of arid inland sources of ions in buffering anthrogenic sources of acidic ions is important at a regional scale. Industrial emissions have produced acid rain at some locations but studies suggest a local problem with few regional influences in Australia, and data show a higher average pH of rainfall than reported in North America and Europe. Emissions of NO x are largely urban, but SO 2 emissions are associated with urban and industrial areas, most notably a relatively small number of very large metal smelting and power generation sites, often in remote arid areas with little rainfall.

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Acid rain and air pollution: 50 years of progress in environmental science and policy

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Murray, F. Acid rain and acid gases in Australia. Arch. Environ. Contam. Toxicol. 18 , 131–136 (1989). https://doi.org/10.1007/BF01056197

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Received : 27 January 1988

Revised : 08 March 1988

Issue Date : January 1989

DOI : https://doi.org/10.1007/BF01056197

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Acid mine drainage in Australia: Its extent and potential future liability

Supervising Scientist Report 125 Harries J Supervising Scientist ISSN 1325-1554 ISBN 0 6422 4325 5

Cover (PDF 154.7KB)

Preliminary pages (PDF 374.4KB)

Section 1 Introduction (PDF 129.4KB)

Section 2 Background (PDF 1.1MB)

Section 3 Survey of acid mine drainage at mine sites in Australia (PDF 846.9KB)

Section 4 Estimate of liability for current mines (PDF 447.7KB)

Section 5 Liability of historic mine sites (PDF 441.7KB)

Section 6 Discussion and recommendations (PDF 894.6KB)

Section 7 Conclusions (PDF 70.5KB)

References (PDF 320KB)

Appendices (PDF 1.2MB)

About the report

The oxidation of sulphidic mine wastes and the consequent release of acid mine drainage and acid rock drainage, is one of the main strategic environmental issues facing the mining industry. The production of broken waste rock and tailings by mining operations can expose large amounts of pyrite and other sulphides to the effects of water and oxygen. Sulphides in the walls of opencuts and underground workings are also exposed by the mining process. Despite general agreement on the significance of acid mine drainage at Australian mine sites in terms of its impact on the environment, its extent has not been quantified, and the additional costs of managing acid mine drainage have not been estimated.

In order to better understand the impact of acid drainage in Australia and to provide a basis for assessing long-term management options and strategic research needs, the Office of the Supervising Scientist ( oss ) and the Australian Centre for Minesite Rehabilitation Research (ACMRR) initiated a study to prepare a status report on acid mine drainage in Australia covering both operational and historic sites. The study was supported by the Minerals Council of Australia.

Information was collected from mine site staff, government department officials and others in Australia who have expertise in the characterisation and management of sulphidic mine wastes. Questionnaires were sent to 317 mine sites considered to be sites where the excavated material could be acid generating. The questionnaires sought information about surface water management, ground water, open cuts, underground workings, water qualities, acid base accounting and the types and amounts of potentially acid generating wastes. Information was also collected on historic mine sites where acid drainage was known to be a problem.

Results from the survey suggest that about 54 sites in Australia are managing significant amounts of potentially acid generating wastes, where significant amounts means more than 10% of the wastes is potentially acid generating or there is more than 10 million tonnes (Mt) of potentially acid generating wastes. About 62 additional sites are managing some potentially acid generating wastes but less than 10% of the total wastes and less than 10 Mt.

The most common approach to managing sulphidic wastes is to install a low-permeability cover over the wastes and/or encapsulating the wastes within non-sulphidic materials. In some cases the low permeable covers are constructed by compacting other mine wastes. The average cost of covering potentially acid generating at currently operating mine sites is estimated to be about $40 000 ha -1 .

For the Australian industry as a whole, the additional cost of managing potentially acid generating wastes at operating mine sites is estimated to be about $60 million per year. This includes the costs of cover installation, selective placement of wastes, additional waste characterisation and water treatment as appropriate. Over 15 years, the total cost of managing potentially acid generating mine wastes from current mines is $900 million (1997 dollars) for the whole industry.

Costs of managing acid generating wastes are much greater if sulphide oxidation and release of pollutants is discovered after mine closure. The costs of remediating historic mine sites releasing acid mine drainage are $100 000 or more per hectare, and these costs would also apply to mine sites where acid drainage is discovered late in mine life or after mine closure. The costs of treating contaminated water-filled voids or seepages from adits would be additional.

These estimated Australian costs are significantly less that the C$2 to C$5 billion total liability costs for potentially acid generating wastes at mine sites in Canada estimated by the Canadian Mine Environment Neutral Drainage (MEND) program. The Canadian liability represents the cost of remediating the currently estimated inventory of acid generating wastes in Canada. The amount of potentially acid generating mine wastes in Canada is similar to the amount in Australia, but the estimated costs of remediation for Canadian sites is three to five times greater than for Australian sites.

The management of potentially acid generating wastes is an important environmental issue; major costs may arise late in mine life or after mine closure if proper waste management strategies are not in place from the beginning of mine operations. The risk of these increased costs late in mine life should be of concern to mine owners. Furthermore, the governments will want to ensure that as far as possible the environmental risks and financial liabilities are minimised and are not transferred to government or the community as a result of poor management of the problem during the life of the mine.

The following recommendations cover four main issues: rehabilitation technologies, mine planning, waste characterisation and technical awareness of acid drainage issues.

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EPA Home » Science Inventory » Science and Policy Interactions: A Case Study with Acid Rain

Science and Policy Interactions: A Case Study with Acid Rain

RINGOLD, P. L. Science and Policy Interactions: A Case Study with Acid Rain. Presented at Oral presentation to a class at the Atkinson Graduate School of Management, Willamette University, Salem, OR, October 14, 2010.

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Management of air pollution has a long history in the United States. A succession of laws, with the first Federal law, passed in 1955, has lead to substantial reductions in emissions and improvements in air quality.

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Management of air pollution has a long history in the United States. A succession of laws, with the first Federal law, passed in 1955, has lead to substantial reductions in emissions and improvements in air quality. These laws were simulated originally by acute local effects on human health and ecosystems, but have increasingly been designed to reduce chronic regional effects as well. While analyses show that benefits substantially exceed control costs, the control costs imposed on industries, governments and individuals are substantial. As a result, there has been and continues to be an intimate connection between science and policy in the management of air pollution. A general model showing an idealized relationship between science and policy will be developed and illustrated by examining acid rain research and management. Attention was first drawn to acid rain in the early 1970’s with calls for research and policy attention. In 1979 and interagency effort, the National Acid Precipitation Assessment Program, was established to coordinate research across federal government necessary to inform policy. The ten year program eventually expended $600 million and provided numerous policy relevant reports. As a result of NAPAP research, the clean Air Act Amendment of 1990 developed a program to control acid rain. In contrast to previous “command and control” approaches to manage pollution, and in contrast with approaches considered during policy deliberation throughout the 1980’s, Congress chose to manage acid rain with an innovative cap and trade approach. As a result emissions have been reduced at costs much lower than con template. Continuing monitoring programs show that the aquatic effects of acid rain have been lessened. Economic analyses show that the benefits are about 40 times greater than the control costs. The cap and trade approach is often discussed in deliberations on other pollutants including green house gases.

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